organic chemisty_reaction mechanisms

1. (a) What is meant by a chiral compound?

....................................................................................................................................

.................................................................................................................................... (1)

(b) Substitution reactions of halogenoalkanes can proceed via an SN1 or SN2 mechanism. In the case of SN1, a chiral halogenoalkane does not give a chiral product.

(i) Give the equation for the reaction between 2-bromobutane and aqueous hydroxide ions, using structural formulae.

(ii) Give the mechanism for this SN1 reaction.

(iii) Explain why the product is not chiral.

..........................................................................................................................

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.......................................................................................................................... (8)

(c) In an experiment designed to find the mechanism of the reaction between a halogenoalkane, RX, and hydroxide ions, the following data were obtained at constant temperature.

Initial concentration ofRX/mol dm

0.01

0.01

0.005

Initial concentration ofOH /mol dm

0.04

0.02

0.04

8 10

4 10

4 10

6

6

6

33 Initial rate/mol dm s3 1

(i) Deduce the order with respect to RX and OH and hence write the rate equation for the reaction.

Khalid Mazhar Qureshi www.edexcel-cie.com

(ii) Calculate a value for the rate constant for the reaction.

(4)

(d) How does the rate of nucleophilic substitution of halogenoalkanes, RX, change with the halogen in the compound? Give reasons for your answer.

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (3)

(Total 16 marks)

2. Substitution reactions of halogenoalkanes can proceed via an SN1 or SN2 mechanism. In the case of SN1, a chiral halogenoalkane does not give a chiral product.

(i) Give the equation for the reaction between 2bromobutane and aqueous hydroxide ions, using structural formulae.

(ii) Give the mechanism for this SN1 reaction.

(iii) Explain why the product is not chiral.

..........................................................................................................................

..........................................................................................................................

.......................................................................................................................... (8)


3. In an experiment designed to find the mechanism of the reaction between a halogenoalkane, RX,

and hydroxide ions, the following data were obtained at constant temperature.

Initial concentration ofRX/mol dm

0.01

0.01

0.005

Initial concentration ofOH /mol dm

0.04

0.02

0.04

8 10

4 10

4 10

6

6

6

33 Initial rate/mol dm s3 1

(i) Deduce the order with respect to RX and OH and hence write the rate equation for the reaction.

(ii) Calculate a value for the rate constant for the reaction.

(4)

4. (a) The enthalpy change for the reaction

CH2CH2 + H2 CH3CH3 is 120 kJ mol1, whereas that for the reduction of benzene, C6H6, to cyclohexane, C6H12,

is 208 kJ mol1. What may be deduced from the fact that this value is not three times the first one?

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

(b) (i) State the conditions under which benzene may be nitrated to form mononitrobenzene.

..........................................................................................................................


(ii) Both of the reagents that are used to nitrate benzene are usually regarded as acids.

However, in this instance, one of them behaves as a base. Show how this is so.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

(iii) Give the mechanism for the nitration of benzene.

(iv) Explain why benzene tends to undergo substitution rather than addition reactions.

..........................................................................................................................

.......................................................................................................................... (8)

(Total 10 marks)

5. (i) State the conditions under which benzene may be nitrated to form mononitrobenzene.

..........................................................................................................................

(ii) Both of the reagents that are used to nitrate benzene are usually regarded as acids. However, in this instance, one of them behaves as a base. Show how this is so.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

(iii) Give the mechanism for the nitration of benzene.

(iv) Explain why benzene tends to undergo substitution rather than addition reactions.

..........................................................................................................................

.......................................................................................................................... (8)


6. This question concerns 2-bromo-2-methylbutane, CH CH C Br3

3

23

CH

CH which reacts with

aqueous potassium hydroxide solution via an SN1 mechanism.

(a) Show this mechanism and identify the rate determining step. (4)

(b) If the conditions are altered potassium hydroxide will react to give an elimination reaction with the same halogenoalkane.

Draw the structural formula and give the name of an organic product of this elimination reaction, showing all the covalent bonds.

(2)

(c) The product in (b) can be polymerised.

(i) Write the formula for this polymer showing the structure of the repeating unit. (2)

(ii) Suggest why, in terms of the nature of the bonds in such polymers, they are persistent in the environment but are not particularly hazardous.

(2)

(d) The rate equation for the substitution reaction in part (a) is rate = k[2-bromo-2-methylbutane]

(i) State the order of the reaction.

(1)

(ii) If the same halogenoalkane is reacted with cyanide ions instead of hydroxide ions, and all other conditions remain the same, state with reasons whether the rate of the reaction would alter.

(3)

(e) Reaction rates generally increase with an increase in temperature for two reasons.

(i) State what these reasons are.

(2)


(ii) The distribution of molecular energies at a given temperature T1 is shown below.

Sketch on the same axes a graph appropriate to a higher temperature T2, and hence explain why the rate increases.

Number ofmoleculeswith agivenenergy

Energy

(4)

(iii) By using the graph, or otherwise, explain the effect of a catalyst on the rate of a reaction.

(2)

(Total 22 marks)

7. Propenal, CH2=CHCHO, is one of the materials that gives crispy bacon its sharp odour. In the following question assume that the carboncarbon double bond and the aldehyde group in propenal behave independently.


(a) Give the structural formulae of the compounds formed when propenal reacts with:

(i) hydrogen bromide; (2)

(ii) hydrogen cyanide; (1)

(iii) 2,4-dinitrophenylhydrazine. (2)

(b) (i) Give the mechanism for the reaction between hydrogen cyanide and the aldehyde group. You may represent the aldehyde group as

R

HC O

(3)

(ii) The reaction in (i) occurs best in slightly acidic conditions. It is slower if the pH is high or low. Suggest reasons why this is so.

High pH .

Low pH ..

. (3)

(c) Explain why lithium tetrahydridoaluminate(III) (lithium aluminium hydride), LiAlH4, reacts only with the >C=O bond and not with the >C=C< bond, even though these bonds have the same electronic structure.

..

..

.. (2)

(d) Suggest reactions, giving equations and conditions, which would convert propenal into a compound which would react with iodine in the presence of sodium hydroxide solution.

(4) (Total 17 marks)


8. (a) The free radical reaction between methane and chlorine in ultraviolet light has a

mechanism whose initiation step is

Cl2 2Cl

Followed by one of two possible propagation steps

CH4 + Cl CH3 + HCl I CH4 + Cl CH3 Cl + H II

(i) Use the data given below to predict which is the more likely propagation step.

bond enthalpies/kJmol1: ClCl 243; CH 435; HCl 432; CCl 346. (4)

(ii) Identify one product you might expect from a termination step following each reaction that would not be found in the alternative reaction scheme.

I ..

II . (2)

(b) The reaction in part (a) is an important industrial source of hydrochloric acid, HCl(aq). The hydrogen halides HX(aq), sometimes called the hydrohalic acids, are all Brnsted-Lowry acids.

(i) What is a Brnsted-Lowry acid?

(1)

(ii) Explain why HF(aq) is the weakest of these hydrohalic acids.

(2)

(c) Boron trichloride is a gaseous compound which reacts readily with water.

(i) Write an equation for this reaction.

(2)

(ii) Explain why boron trichloride reacts readily with water.

(3)

(Total 14 marks)


9. Two types of reaction in organic chemistry are electrophilic addition and nucleophilic

substitution.

(a) Define the terms:

(i) Nucleophile:

(1)

(ii) Electrophile:

(1)

(iii) Substitution:

(1)

(iv) Addition.

(1)

(b) Give the mechanism of a reaction of your choice which proceeds by electrophilic addition. (3)

(c) (i) Describe, briefly, a reaction you could carry out in the laboratory which occurs by nucleophilic substitution.

(1)

(ii) Write a mechanism for this reaction. (3)

(iii) What type of nucleophilic substitution is occurring in this reaction? Justify your answer.

(1)


(d) When a solution of bromine is shaken with cyclohexene, , the bromine is decolourised. However, when bromine is added to benzene there is no decolourisation.

(i) Write an equation for the reaction of cyclohexene with bromine. (1)

(ii) Explain, in terms of the bonding why no reaction occurs when a solution of bromine is shaken with benzene.

(2)

(Total 15 marks)

10. (a) Outline the reaction of propanone with the following reagents. Give the equation for the reaction, the conditions, and the name of the organic product.

(i) Hydrogen cyanide

Equation:

Conditions:

Name of product:

(3)

(ii) Sodium tetrahydridoborate(III) (sodium borohydride)

Equation (you may represent NaBH4 as [H]):

Conditions:

Name of product: ..

(3)

(b) (i) Give the mechanism for the reaction in (a)(i). (3)

(ii) What type of mechanism is this?

(1)

(iii) What feature of the carbonyl group makes this type of mechanism possible?


Explain how this feature arises.

(2)

(iv) Explain briefly, by reference to its structure, why ethene would not react with HCN in a similar way.

(1)

(Total 13 marks)

11. Benzene reacts with concentrated nitric acid in the presence of concentrated sulphuric acid at about 50 C in an electrophilic substitution reaction to give nitrobenzene.

(a) (i) Give the equation representing the overall reaction. (1)

(ii) Give the equation representing the formation of the electrophile.

(1)

(iii) Give the mechanism for the reaction of the electrophile with benzene. (3)

(b) In an experiment to determine the kinetics of this reaction, it is found that the attack of the electrophile on the benzene ring is the rate determining step. The following data shows the effect of changing the concentrations on the rate:

[benzene](relative)

[electrophile](relative)

Rate(relative)

1 1 11 2 22 1 22 2 4

(i) What is the order with respect to

benzene ..

the electrophile? (2)

(ii) Write a rate equation for the reaction.

(1)

(iii) In some electrophilic substitution reactions of aromatic compounds, the rate determining step is the production of the electrophile. In such cases what would be


the order of the reaction with respect to the aromatic compound?

(1)

(c) The equation representing the hydrogenation of ethene is

H2C CH2+H2 H3CCH3 H = 120 kJ mol1

(i) Assuming that benzene consists of a ring with three double bonds, predict the enthalpy change for the reaction

+ 3H 2

(1)

(ii) The enthalpy of hydrogenation of benzene is actually 205 kJ mol1. What can you deduce from this and your answer to part (i) about the stability of the benzene ring? Use an enthalpy level diagram to illustrate your answer.

(2)

(iii) The compound cyclooctatetraene

has an enthalpy of hydrogenation of 480 kJ mol1; the molecule, unlike that of benzene, is not flat. Suggest in terms of the possibility of orbital overlap why cyclooctatetraene does not show the same type of stability as benzene, despite superficial similarities in their structures.

(2)

(Total 14 marks)

12. Sodium hydroxide is a very important substance. Potassium hydroxide is also important but it is produced in smaller quantities and is costlier. For some purposes, potassium hydroxide is necessary; it will take part in substitution, elimination, hydrolysis, acidbase and redox processes.

(a) Suggest how potassium hydroxide is manufactured. A detailed account of the manufacturing plant is not required.

(3)


(b) (i) Potassium hydroxide can be used in substitution reactions with halogenoalkanes.

2bromo2methylpropane is known to react with hydroxide ions via an SN1 mechanism. Give the rate equation for the reaction, and justify it by giving the mechanism and explaining the relationship between the rate equation and the mechanism. What is the role of the hydroxide ions in this reaction?

(6)

(ii) The halogenoalkane could contain chlorine, bromine, or iodine. Explain what effect, if any, the nature of the halogen has on the rate of the reaction.

(2)

(c) Potassium hydroxide is used for elimination reactions of halogenoalkanes because it is more soluble in the solvent ethanol than sodium hydroxide is. 2Bromobutane gives two organic products when reacted with potassium hydroxide in ethanol, one of these having two stereoisomers. Give structural formulae for all three product molecules and explain the existence of the stereoisomeric forms in terms of the orbitals involved. What is the role of the hydroxide ions in this reaction?

(6)

(d) Tristearin is an ester found in animal fats, especially beef tallow, which can be hydrolysed by potassium hydroxide solution. Write an equation to represent the reaction, and state the importance of the potassiumcontaining product.

C H COOCH

C H COOCH

C H COOCH

17

17

17

35

35

35

2

2

Tristearin (4)

(e) Potassium hydroxide solution reacts with chlorine at room temperature.

Write the ionic equation for this reaction and explain the nature of the reaction. (4)

(Total 25 marks)

13. The reactions of chlorine are important in both inorganic and organic chemistry, the chemistries of the resulting compounds also being linked.

(a) Chlorine reacts with aluminium in a similar fashion to its reaction with iron.

(i) Sketch an apparatus which you could use to make aluminium chloride from aluminium and dry chlorine, indicating one safety precaution specific to this reaction.

(3)

(ii) Explain in terms of bonding and structure why aluminium chloride sublimes and has a relative molecular mass of 267.

(3)


(iii) Show by means of ionic equations why dissolving aluminium chloride in water

produces an acidic solution. By further consideration of the equilibria present explain why the addition of aqueous sodium hydroxide solution results initially in a white precipitate, which dissolves upon further addition of sodium hydroxide.

(6)

(iv) Aluminium was first produced by the reaction of sodium with aluminium chloride. Write an equation representing the reaction and explain why, although it is apparently simpler than the electrolysis of purified bauxite it is not more economical.

(2)

(b) Aluminium chloride is used as a catalyst in the reaction of benzene with chloromethane. The methylbenzene produced can then itself react with chlorine in one of two ways, depending on the conditions:

C H Cl

C H Cl (three isomers)

C H Cl C H Cl7

7

7

7

7 6 2 7 5 3Clu.v.

Cl

Cl

u.v.

Clu.v.

2

2

2

AlCl3

AlCl 3

2

P

S

Q R

+ CH Cl3

(i) Suggest a mechanism for the reaction of chloromethane with benzene. (4)

(ii) Suggest a structural formula for any one of the three isomers of compound S produced by the reaction shown.

(1)

(c) Compound Q has both chlorine atoms attached to the same carbon atom.

(i) Draw the structure of Q. (1)


(ii) Q will react with sodium hydroxide solution under suitable conditions in a

nucleophilic substitution reaction, both chlorine atoms being substituted. It might therefore be expected that the product will contain the structure.

C OH

H

OH

In practice, this reacts further to give an aldehyde and water. Use the bond enthalpies given to suggest why this is so.

Bond enthalpy/kJ mol1 C O C H C O H O

358 413 736 464 (4)

(iii) Suggest the structure of the product when R is reacted with sodium hydroxide solution.


14. This question concerns the compound, Q pent-3-en-2-ol

CH CHCH CHCH

OH3 3

(a) Give the structural formula of a compound isomeric with Q which does not contain a carbon-carbon double bond.

(1)

(b) Q shows two -types of stereoisomerism.

(i) Draw the geometric isomers of Q, and state why Q shows this type of isomerism.

...........................................................

........................................................... (2)


(ii) Draw the optical isomers of Q and state what effect such isomers have on the plane

of plane polarised monochromatic light.

...........................................................

........................................................... (3)

(c) Give the mechanism for the reaction of bromine with Q; you may represent the compound in this margin as >C=C< for the purposes of this question.

(3)

(d) (i) Give the structural formula of the product obtained when Q is reacted with potassium dichromate(VI) solution in the presence of dilute sulphuric acid.

(1)

(ii) Describe a test to show that the product formed in (i) is not an aldehyde. Suggest a positive test which would give the identity of the new functional group which is present in the molecule, and state what you would see.

...........................................................

...........................................................

...........................................................

........................................................... (4)


(e) The iodine number is a measure of the degree of unsaturation of a molecule. It relates to

the number of double bonds it contains. It is defined as the number of grams of iodine, I2, that react with I g of the compound.

Show that the iodine number of Q is approximately 3 by calculating the number of grams of iodine, which react with I g of Q.

(3)

(Total 17 marks)

15. (a) Ethane reacts with chlorine in the presence of ultraviolet light,

(i) What is the function of the u.v. light?

........................................................... (1)

(ii) The reaction gives more than one chlorine-containing organic product.

Explain why this is so.

...........................................................

........................................................... (1)

(iii) State the name of one other product formed in this reaction which does not contain chlorine and account for its formation.

...........................................................

...........................................................

...........................................................

........................................................... (3)

(b) Methylbenzene reacts with chlorine in the presence of u.v. light in a similar way to methane:

+ Cl + HCl2

3 2CH CH Cl

In order for the reaction to take place, chlorine must be passed into boiling methylbenzene in the presence of u.v. light over a period of time.


(i) Draw an apparatus which could be used for this reaction

(3)

(ii) What are the hazards specific to this experiments

...........................................................

........................................................... (2)

(iii) Assuming that the organic product from this reaction consists only of methylbenzene and (chloromethyl)benzene, and that Raoult's Law applies to the mixture of the two liquids, sketch a boiling-point/composition diagram for the mixture and use it to show how fractional distillation enables the components of the mixture to be separated. Methylbenzene boils at 111oC, (chloromethyl)benzene at 179C.

179 C

111 C

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...........................................................

........................................................... (4)

(Total 14 marks)

16. The kinetics of a reaction are used to clarify reaction mechanisms. An experiment to determine the kinetics of the substitution reaction between 2-chloro-2-methylpropane and sodium hydroxide uses equal initial concentrations of these substances in aqueous ethanol solvent. A mixture was maintained at 25C, and samples taken at intervals. The samples are quenched in about twice their volume of cold propanone, and the concentration of sodium hydroxide is found.

Time/min:

Conc. mol dm

0

0.080

7

0.065

15

0.054

27

0.041

44

0.028

60

0.0203


(a) (i) Show by means of a suitable graph that the reaction is first order.

(4)

(ii) As performed, the results cannot distinguish between the rate laws

rate = k[OH] and rate = k[halogenoalkane]

Outline a further experiment which must be performed to enable the distinction to be made, showing how the new data would be used to establish the rate law.

(3)

(iii) The reaction is in fact first order with respect to the halogenoalkane. Write the mechanism for the substitution reaction, identifying the rate-determining step.

(4)

(iv) Nucleophilic substitution is usually accompanied by elimination as a competing reaction. Write the name and structural formula of the product of the elimination reaction with 2-chloro-2-methylpropane and state the conditions which favour elimination over substitution

(3)

(b) The method of preparation of 2-chloro-2-methylpropane reverses the above substitution reaction. A modified version of part of the method is given below.

Place 25 g of 2-methylpropan-2-ol and 85cm3 of concentrated hydrochloric acid in a stoppered separating funnel.

Shake the mixture periodically over 20 minutes, releasing the pressure from time to time.

Allow the layers to separate, draw off and discard the lower acid layer. Wash the organic layer with 20 cm3 of 5% NaHCO3 solution, and then with water;

discard the aqueous layer in each case.

Add 5g of anhydrous calcium sulphate to the organic layer. Filter the organic layer into a dry distillation apparatus, and distil; collect the fraction

between 49 C and 51 C. The yield is 28 g (90%). The first step in the mechanism for this reaction involves protonation of the hydroxyl group of the alcohol.

(i) Representing the alcohol as ROH, use dot-and-cross diagrams to show the structure of the protonated alcohol, and suggest why this species is substituted by a chloride ion whereas in the absence of acid the reaction does not work.

(4)

(ii) Explain why the organic product is treated with sodium hydrogen carbonate solution, then with water, and then with anhydrous calcium sulphate. Show, on the basis of the quantity of alcohol used, that the yield of the product is 90% as claimed, and give reasons why the yield is less than 100%.



17. (a) Ammonia is manufactured by passing hot nitrogen and hydrogen at high pressure over a

catalyst containing iron.

In an experiment, 9.0 moles of nitrogen and 27 moles of hydrogen were put into an iron vessel of volume l0 dm3. This was then heated to 250 C and allowed to reach equilibrium. It was found that two thirds of the nitrogen and hydrogen were converted into ammonia.

N2(g) + 3H2(g) 2NH3(g) H = 92.4 kJ moll (i) Give the expression for Kc.

(1)

(ii) Complete the table below.

N2 H2 NH3

moles at start 9.0 27 0

moles at equilibrium

concentration at equilibrium /mol dm3

(2)

(iii) Calculate the value of Kc at 250 C, stating its units.

(2)


(iv) State the effect, if any, of an increase in temperature on the value of the

equilibrium constant, giving a reason.

....

....

.... (2)

(v) State the effect, if any, of an increase in pressure on the value of the equilibrium constant, giving a reason.

....

....

.... (2)

(b) Some of the ammonia manufactured in this way is converted into nitric acid, HNO3. The first step in this process is the oxidation of ammonia.

4NH3(g)+ 5O2(g) 4NO(g) + 6H2O(g) (i) Calculate the standard enthalpy change for this reaction given the following

standard enthalpies of formation in kJ mol1:

NH3(g) 46.2 NO(g) + 90.4 H2O(g) 242

(3)

(ii) Draw an enthalpy level diagram for this reaction.

Enthalpy

(2)


(c) A mixture of concentrated nitric and sulphuric acids is used in the nitration of benzene to

form nitrobenzene.

(i) The first stage of the reaction is the production of the NO 2 ion

Write an equation to show its formation.

.... (1)

(ii) The formation of the NO 2 ion occurs in two steps, the first of which is:

H2SO4 + HNO3 H2NO 3 + HSO 4 This is an acid/base reaction. Give the formulae of the acid/base conjugate pairs

involved.

acid . its conjugate base .

base . its conjugate acid . (2)

(iii) Hence comment on the relative strengths of nitric and sulphuric acid.

.... (1)

(iv) Give the mechanism for the reaction of the NO 2 ion with benzene.

(3)

(v) What do curly arrows show when used in a mechanism?

(1)

(Total 22 marks)


18. When 1,2-dibromoethane is warmed with sodium iodide dissolved in propanone at 50 C,

ethene, sodium bromide and iodine are produced:

BrCH2CH2Br + 2NaI CH2==CH2 + I2 + 2NaBr (a) A study of the kinetics of this reaction at a particular temperature gave the

following results

Experiment [BrCH2CH2Br]/mol dm3

[I] /mol dm3

Initial rate of reaction (relative)

A 0.01 0.01 1

B 0.01 0.02 2

C 0.02 0.01 2

D 0.02 0.02 4

(i) What is the order of reaction with respect to 1,2-dibromoethane? Give your reasoning.

(2)

(ii) What is the order of reaction with respect to sodium iodide? Give your reasoning. (2)

(iii) State the overall order of the reaction. (1)

(iv) Suggest what the first step in the reaction mechanism might be, giving your reasons. The detailed mechanism for the reaction is not expected.

(2)

(v) Explain why the mechanism for the reaction must contain at least two steps. (2)

(b) Propanone is chosen as the solvent because iodine, 1,2-dibromoethane and sodium iodide are soluble in it; sodium bromide is not.

(i) By considering this information and the equation for the reaction say what you would expect to see as the reaction proceeds.

(2)

(ii) In such a reaction, 15.7 g of 1,2-dibromoethane (Mr = 188) was used initially. Assuming complete reaction, what volume of ethene (in cm3) would be produced? The volume of 1 mole of gas at the temperature and pressure of the experiment is 24 dm3 Assume that ethene is not significantly soluble in propanone.

(3)


(iii) The progress of the reaction could be followed by titrating the liberated iodine with

sodium thiosulphate solution. Describe how you would perform such titrations on portions of the reaction mixture.

(6)

(iv) Calculate the volume of 1.00 mol dm3 sodium thiosulphate solution required to titrate one-tenth of the reaction mixture in (ii) after the reaction was completed.

(3)

(v) The solubility of sodium iodide in propanone suggests that it has somewhat more covalent character than sodium bromide, which is not soluble. Suggest why the bonding in the two salts is different.


19. Chlorine forms oxyacids such as HOCl. Until 1973 HOF was believed not to exist.

(a) (i) Give the equation for the reaction of chlorine with water at room temperature. By considering oxidation states explain why this is a disproportionation reaction.

(3)

(ii) If sodium hydroxide solution is added to the solution of chlorine in water from (i) and the mixture is heated, a further disproportionation reaction occurs. Write an ionic equation to represent this further reaction, and hence show that chlorine reacts with hot sodium hydroxide solution to give the two chlorine-containing products in a mole ratio of 5 to 1.

(3)

(b) HOF is a covalent substance.

(i) Draw a dot-and-cross diagram for HOF. (1)

(ii) State and explain the shape of the molecule. (2)

(iii) Suggest why the oxidation state of F in HOF cannot be the same as that of Cl in HOCl.

(2)

(c) At room temperature HOF decomposes as follows:

HOF(g) HF(g) + O2(g) The reaction is first order with respect to HOF and has a half-life of 30 minutes.

(i) Write the rate equation for the reaction,

(ii) Approximately how long would it take for the concentration of HOF to fall to 1.5% of its initial value?

(2)


(d) HOF is made by the following reaction:

F2(g) + H2O(s) 40C HOF(g) + HF(g)

HOF must be rapidly removed from the reaction site since it reacts with HF, F2 and water. The apparatus is made from poly(l-chloro-1,2,2-trifluoroethene).

(i) Draw the structural formula of 1-chloro-1,2,2-trifluoroethene. (1)

(ii) Draw enough of the polymer chain formed by this material, to make the repeating structure clear.

(2)

(iii) Suggest, in terms of the nature of polyhalogenated hydrocarbons, why this polymer is used for the apparatus for synthesis of HOF.

(3)

(e) Organic fluorine compounds are often different from their analogues with other halogens.

(i) Chloromethane reacts with a solution of hydroxide ions in an SN2 reaction. Give the mechanism for this reaction.

(3)

(ii) Given the following bond lengths

CCl 0. 177 nm CF 0.139 nm

suggest why fluoromethane does not react with a solution of hydroxide ions. (2)

(Total 25 marks)

20. (a) Some standard enthalpy change of combustion values are listed below:

Substance H /kJ mol1 C (graphite) 393.5

H2(g) 285.8

ethane C2H6(g) 1560.0

(i) Define standard enthalpy change of combustion

............................................................................................................................

............................................................................................................................ (2)

(ii) Complete the following thermochemical equation for the standard enthalpy change of combustion of ethane.

..C2H6(..)+..O2(..) ..CO2(..)+..H2O(..) H =............................................ (3)


(iii) Use the data to calculate the standard enthalpy change of formation of ethane.

Draw a Hesss Law cycle as part of your answer.

(3)

(b) Consider the reaction

C2H6(g) + Cl2(g) C2H5Cl(g) + HCl(g) H = 112.6 kJ mol1

This reaction does not proceed at room temperature in the absence of light, but reacts rapidly when exposed to a bright light. Use these facts to illustrate the concept of thermodynamic and kinetic stability.

Thermodynamic stability ...........................................................................................

....................................................................................................................................

Kinetic stability .........................................................................................................

.................................................................................................................................... (2)

(c) Ethane and chlorine react in a homolytic free radical substitution reaction when exposed to light. The two propagation steps are

step 1:

C H + Cl CH C + H Cl

H H

H H

CH 3 3

step 2

C + + Cl Cl Cl CH C Cl

H H

H H

CH 3 3

(i) Explain the meaning of the term free radical.

............................................................................................................................ (1)

(ii) Explain the meaning of the term substitution reaction.

............................................................................................................................ (1)

(iii) Explain the movement of the C-H bond electron pair in step 1.

.........................................................................................................................

......................................................................................................................... (2)

(iv) Give an example of a possible termination step in this reaction.


......................................................................................................................... (1)

(d) The reaction of ethane with bromine proceeds in a similar way. Given the following average bond enthalpies in kJ mol1

CH + 412 HBr + 366

calculate the enthalpy change for step 1 of the reaction involving bromine.

(2)

(e) The product of bromination of ethane is bromoethane. This reacts with potassium cyanide in a solution of ethanol and water. The rate of this reaction was studied and the results are given below.

Experiment [CN]/mol dm3 [C2H5Br]/mol dm3 Initial rate/mol dm3s1

1 0.060 0.020 1.0 105

2 0.060 0.040 2.0 105

3 0.120 0.020 2.0 105

Deduce, showing your reasoning, the rate equation.

(3)

(f) Two routes can be suggested for the reaction in (e).

Route 1

CN + CH CH Br NC C Br CH CH CN + BrH

H

CH

3 3

3

2 2.... ..........

Route II

CH CH Br CH CH + Br3 32 2slow + then CH CH + CN CH CH CN3 32 2fast+


(i) Explain which route is consistent with the rate equation in (e).

...........................................................................................................................

........................................................................................................................... (1)

(ii) This exothermic reaction is catalysed by iodide ions. Draw the enthalpy level diagram for both the uncatalysed reaction, labelling each clearly.

enthalpy

(3)

(Total 24 marks)

21. Ethyl benzene is prepared by the reaction between bromoethane and benzene, using anhydrous aluminium bromide as a catalyst in a solution of ethoxyethane (ether). After the reaction is complete the ether and any unreacted bromoethane are distilled off. Finally the ethyl benzene and unreacted benzene are separated by fractional distillation.

(a) Suggest the mechanism for the reaction between benzene and bromoethane.

(4)


(b) Benzene (boiling temperature 80C) and ethyl benzene (boiling temperature 136C)

dissolve in each other and form solutions which obey Raoults Law.

Draw a boiling temperature/composition diagram, labelling the liquid and vapour lines. Use your diagram to explain what happens when a mixture containing 40% benzene and 60% ethylbenzene is fractionally distilled.

Boiling temperature /C

% composition

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (6)

(c) Give the reagents and conditions necessary for the conversion of ethyl benzene, C6H5CH2CH3, into potassium benzoate C6H5COOK.

Reagents ....................................................................................................................

....................................................................................................................................

Conditions .................................................................................................................

.................................................................................................................................... (3)

(Total 13 marks)

22. (a) Give the principles which enable you to predict the shape of a particular molecule, given its formula. Draw dot-and-cross diagrams for SiCl4 and XeF4, and hence draw the shapes of each of these molecules.

(6)


(b) When 2-bromopropanoic acid, CH3CH(Br)COOH, is reacted with sodium hydroxide in

aqueous solution, 2-hydroxypropanoic acid is formed. The reaction takes place by an SnI mechanism.

(i) Write an equation for the reaction between 2-bromopropanoic acid and hydroxide ions.

(1)

(ii) Explain why 2-bromopropanoioc acid can show optical isomerism. State how this could be detected.

(2)

(iii) If a single optical isomer of 2-bromopropanoic acid is reacted with sodium hydroxide, the resulting 2-hydroxypropanoic acid mixture is not optically active. Write a reaction mechanism for the reaction, and explain why optical activity is lost.

(5)

(c) Optical activity is not confined to organic compounds; chirality is also seen in some chromium compounds. 1,2-diaminoethane, H2NCH2CH2NH2, forms an octahedral complex with chromium (III) ion. This complex ion [Cr(H2NCH2CH2NH2)3]3+ is chiral, and the structure of one isomer is shown below.

Cr+

N

N

NN

NN

where 1,2-diaminoethane is shown as N N.

Sketch the structure of the other isomer and say why the complex ion is chiral. (2)

(d) A student was given a chromium compound Z to analyse. The following information was obtained:

Z was orange; a solution of Z acidified with sulphuric acid converted propan 2-ol to propanone; a solution of Z, acidified with sulphuric acid, reacted with a solution of iron(II) ions in a 1 : 6 molar ration Z:Fe2+ to give a green solution;

on heating an alkaline solution of Z, ammonia was evolved; Account as fully as you can for the above observations and identify Z.



23. One of the isomers of C4H10O is the alcohol 2-methylpropan-2-ol which has the structural

formula

OH

CH

CH CHC

3

3 3

(a) There are three other structural isomers of C4H10O which are also alcohols.

(i) Draw their structural formulae.

(3)

(ii) One of these isomers exhibits stereoisomerism. Name the type of isomerism shown and draw diagrams showing clearly how these stereoisomers differ from one another.

Type of isomerism .........................................................................................

Diagrams of isomers

(3)


(iii) Describe a test to show that each of the isomers in (i) contains an OH group.

......................................................................................................................

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(b) Draw the structural formula of the final organic product of the reaction when each of the three alcohols in (a)(i) is heated under reflux with a solution of potassium dichromate(VI) in dilute sulphuric acid.

ALCOHOL STRUCTURAL FORMULA OF PRODUCT

(3)


(c) 2-methylpropan-2-ol can be prepared by the reaction of 2-bromo-2-methylpropane with

dilute aqueous potassium hydroxide.

(i) Give the mechanism for this reaction.

(3)

(ii) If a concentrated solution of potassium hydroxide in ethanol is used instead of dilute aqueous potassium hydroxide, a different organic product is obtained. Draw the structural formula of this product.

(1)

(Total 15 marks)

24. (a) Define:

(i) the standard enthalpy of formation of benzene, C6H6(l);

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(ii) the standard enthalpy of combustion of benzene, C6H6(l).

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)


(b) Calculate the standard enthalpy of formation of benzene, C6H6(l), using the following

enthalpy of combustion data:

Substance Hc /kJ mol1 C6H6(l) 3273

H2(g) 286

C(s) 394

(3)

(c) If the standard enthalpy of formation is calculated from average bond enthalpy data assuming that benzene has three C==C and three CC bonds, its value is found to be +215 kJ mol1. Explain, with reference to the structure and stability of benzene, why this value differs from that calculated in (b). Use an enthalpy level diagram to illustrate your answer.

................................................................................................................................

................................................................................................................................

................................................................................................................................ (4)


(d) Benzene reacts with bromine when gently warmed in the presence of a catalyst of

anhydrous iron(III) bromide.

(i) The reaction is first order with respect to benzene and first order with respect to bromine. Write the rate equation for the reaction.

...................................................................................................................... (1)

(ii) The mechanism of this reaction involves an attack by Br+ followed by loss of H+.

+

+

+

+

BrH

H

Br

BrBr +H

Step 1.

Step 2.

Deuterium, symbol D, is an isotope of hydrogen, and the CD bond is slightly stronger than the CH bond. If step 2 were the rate-determining (slower) step, suggest how the rate of this reaction would alter if deuterated benzene, C6D6, were used instead of ordinary benzene, C6H6, and explain your answer.

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(Total 14 marks)

25. (a) Consider the following reaction scheme.

CH CHOethanal

3

3

3 3 32 2 2

CH CH(OH)CN

CH CH OH CH CH Br CH CH CNstep 1

step 4

step 2 step 3


(i) State the reagents and conditions for:

Step 1 Reagents .............................................................................................

Conditions ...........................................................................................

Step 2 Reagents .............................................................................................

Conditions ...........................................................................................

Step 3 Reagents .............................................................................................

Conditions ........................................................................................... (7)

(ii) Give the mechanism in step 4 which is the reaction between ethanal and hydrogen cyanide.

(3)

(iii) What type of mechanism is this?

...................................................................................................................... (1)

(iv) State and explain the conditions necessary for step 4.

......................................................................................................................

...................................................................................................................... (2)


(b) The nitrile group, CN, can also be introduced into a molecule by dehydration of an

amide. Outline a reaction scheme, giving names or formulae for the reagents, for the preparation of ethanonitrile, CH3CN, from ethanal, CH3CHO.

(7)

(Total 20 marks)

26. (a) The kinetics of the hydrolysis of the halogenoalkane RCH2Cl with aqueous sodium hydroxide (where R is an alkyl group) was studied at 50 C. The following results were obtained:

Experiment [RCH2Cl] [OH] Initial rate/mol dm3 s1

1 0.050 0.10 4.0 104

2 0.15 0.10 1.2 103

3 0.10 0.20 1.6 103

(i) Deduce the order of reaction with respect to the halogenoalkane, RCH2Cl, and with respect to the hydroxide ion, OH, giving reasons for your answers.

......................................................................................................................

......................................................................................................................

......................................................................................................................

...................................................................................................................... (4)

(ii) Hence write the rate equation for the reaction.

...................................................................................................................... (1)


(iii) Calculate the value of the rate constant with its units for this reaction at 50 C.

(2)

(iv) Using your answer to part (ii), write the mechanism for this reaction.

(3)

(b) (i) Write the equation for the reaction of concentrated sulphuric acid with solid sodium chloride.

...................................................................................................................... (1)

(ii) When concentrated sulphuric acid is added to solid sodium bromide a different type of reaction occurs. Explain why the reactions are different. Identify the gases produced with sodium bromide and write an equation to show the formation of these gases.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

...................................................................................................................... (4)

(Total 15 marks)

27. (a) Ethene reacts with bromine as follows:

C2H4 + Br2 + C2H4Br2 (i) State the conditions necessary for ethene to react with bromine.

...................................................................................................................... (1)


(ii) Give the name of the product.

...................................................................................................................... (1)

(iii) Using the bond enthalpy data below, calculate the enthalpy change for the reaction.

Bond

Bond enthalpy/ kJmol1

CC +348

C==C +612

CH +412

CBr +276

BrBr +193

(3)

(iv) The enthalpy change for this reaction found using the enthalpies of formation of ethene and the product is 90 kJ mol1 - Suggest which value is more likely to be accurate and explain your answer.

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(b) Give the mechanism for this reaction.

(3)


(c) The product, C2H4Br2, is a typical bromoalkane. Suggest the structural formulae of each

of the products of the reaction of C2H4Br2 with the reagents given below and identify the type of reaction involved.

(i) Aqueous sodium hydroxide

Product

Type of reaction................................................................................................ (2)

(ii) Sodium hydroxide in ethanol (heated under reflux)

Product

Type of reaction................................................................................................ (2)

(d) Suggest, giving the reagents and conditions, how compound A could be converted in two steps into compound B.

C C H C C CN

CH CH3 3 3 3

H H H

CH CH

HA B

Step 1.......................................................................................................................

................................................................................................................................

Step 2......................................................................................................................

................................................................................................................................ (4)


(e) Molecules of B are chiral.

(i) Explain the term chiral molecule.

......................................................................................................................

......................................................................................................................

...................................................................................................................... (1)

(ii) Draw the optical isomers of B.

(2)

(Total 21 marks)

28. This question concerns reaction sequences for the conversion of propan-1-ol into 2-bromopropane and butanoic acid.

(a) Propan-1-ol, CH3CH2CH2OH, can be converted into 2-bromopropane, CH3CHBrCH3, in two stages.

CH3CH2CH2OH CH3CH==CH2 CH3CHBrCH3 (i) Give the reagents and conditions necessary for the conversion of CH3CH2CH2OH

into CH3CH==CH2

......................................................................................................................

...................................................................................................................... (2)


(ii) Give the reagent and write the mechanism for the conversion of CH3CH==CH2 into

CH3CHBrCH3

......................................................................................................................

(4)

(iii) Briefly explain why 2-bromopropane is the main product of this second reaction rather than 1-bromopropane.

......................................................................................................................

......................................................................................................................

...................................................................................................................... (1)

(b) Butanoic acid, CH3CH2CH2COOH. can be obtained from propan-1-ol in three steps.

2 2 2 22 2 223 3 3CH CH CH OH CH CH CH Br CH CH CH CO HXStep 1 Step 2 Step 3

(i) Suggest the structural formula of X.

...................................................................................................................... (1)

(ii) Give the reagents and conditions for:

Step 1 ...........................................................................................................

......................................................................................................................

Step 2 ...........................................................................................................

...................................................................................................................... (5)

(iii) State the type of reaction taking place in

Step 1.................................................................................................................

Step 3................................................................................................................. (2)

(Total 15 marks)

29. Benzene, C6H6, reacts with ethanoyl chloride, CH3COCl, by an electrophilic substitution


reaction in the presence of aluminium chloride as a catalyst.

(a) Identify the electrophile involved in this reaction and write an equation to show its formation.

................................................................................................................................

................................................................................................................................ (2)

(b) Draw the mechanism for the electrophilic substitution of benzene by ethanoyl chloride.

(3)

(c) Suggest a reaction scheme, stating reagents and conditions, to convert the product of the above reaction into

OH

C H C COOH

CH

5

3

6

(5)

(Total 10 marks)


30. There is considerable concern about the depletion of the ozone layer. Ozone, O3, is constantly

being formed in the upper atmosphere by oxygen molecules reacting with oxygen atoms. These atoms are formed when other oxygen molecules absorb high energy ultra-violet radiation and undergo homolytic bond fission.

O2 O + O [Reaction 1] O + O2 O3 [Reaction 2]

The ozone formed absorbs ultra-violet radiation and breaks down to oxygen molecules and atoms

O3 O2 + O [Reaction 3] Another reaction, which is not light dependent, also removes ozone

O3 + O 2O2 [Reaction 4] Over time the ozone and oxygen concentrations reach a steady state.

(a) (i) What is meant by the term homolytic bond fission? (2)

(ii) Which of these reactions is likely to be an initiation step? (1)

(iii) Use the reactions above to explain what is meant by the term steady state. (3)

(b) Reaction 2 has an enthalpy change of 100kJ mol1 and Reaction 4 an enthalpy change of 390kJ mol1. Assuming that Reactions 1 and 2 are followed by Reaction 4 show how this results in the upper atmosphere warming up by effectively converting light energy into heat energy. Calculate the amount of heat produced per mole of oxygen molecules.

(4)

(c) In the upper atmosphere chlorofluorocarbons, CFCs, such as CCl2F2 break down to give chlorine atoms and these chlorine atoms react with ozone molecules

Cl + O3 ClO + O2 [Reaction 5] (i) Write an equation to show how the ClO radicals can react with oxygen atoms to

form oxygen molecules. (1)

(ii) Use the equations given in (i) and that given for Reaction 5 to explain how the formation of only a few chlorine atoms can cause the removal of a large number of ozone molecules.

(2)


(iii) Reaction 5 is first order with respect to both chlorine atoms and ozone molecules.

Write the rate equation and use it to explain why continual release of CFCs into the atmosphere seems to have an increasing effect on the depletion of the ozone concentration.

(5)

(iv) Suggest TWO reasons why the rates of all the reactions in the upper atmosphere are likely to be slow.

(2)

(d) 2-hydroxy-4-methoxybenzophenone is used in lotions to protect against sunburn caused by ultra-violet radiation.

3C

O

HO

OCH

(i) Suggest the reagents and conditions for the preparation of 2-hydroxy-4-methoxybenzophenone from 3-methoxyphenol. (You need not be concerned about the location of the side chains in the benzene rings.)

(3)

(ii) Suggest why the release of CFCs into the environment may lead to an increase in sales of lotions containing 2-hydroxy-4-methoxybenzophenone.


31. (a) (i) Explain the term homologous series.

......................................................................................................................

......................................................................................................................

...................................................................................................................... (2)

(ii) To which homologous series does ethene, C2H4, belong?

...................................................................................................................... (1)

(b) Draw the full structural formulae, showing all the bonds, for each of the following:

(i) The organic product of the reaction of ethene, C2H4, with aqueous potassium manganate(VII) and sulphuric acid.

(2)


(ii) 3,4-dimethy1hex-2-ene.

(2)

(iii) A repeating unit of poly(propene).

(2)

(c) Ethene reacts with hydrogen chloride gas to form C2H5Cl.

(i) What type of reaction is this?

...................................................................................................................... (2)

(ii) Give the systematic name for C2H5C1.

...................................................................................................................... (1)

(Total 12 marks)

32. (a) Draw the structural formula of:

(i) an alkane with 4 carbon atoms;

(2)

(ii) an alkene with 4 carbon atoms.

(2)


(b) Draw the structural formula of the product(s) of reacting the alkane you have chosen with

chlorine gas.

(2)

(c) Draw the structural formula of the product(s) of reacting the alkene you have chosen with chlorine gas.

(2)

(d) The reaction of an alkene with bromine is used as a test for alkenes. Describe in detail how you would carry out this test and what you would see if the test proved to be positive.

....

....

....

....

....

.... (3)


(e) Ethene, C2H4 can be converted to a polymer called poly(ethene).

(i) Draw the structure of part of the poly(ethene) molecule clearly showing the repeating unit.

(2)

(ii) Classify the reaction for the formation of poly(ethene) from ethene as one of:

free radical addition,

electrophilic addition,

hydrolysis or oxidation.

.. (1)

(iii) Give one use of poly(ethene).

.. (1)

(Total 15 marks)

33. In this question you will need to use some or all of the following terms

heterolytic homolytic electrophilic/electrophile nucleophilic/nucleophile free radical addition substitution oxidation catalysis


(a) Explain the meaning of the following terms.

(i) Electrophile.

..

..

..

.. (2)

(ii) Nucleophile.

..

..

.. (2)

(b) Explain the difference between heterolytic and homolytic bond breaking.

....

....

....

.... (2)

(c) Classify the following reactions using the terms listed at the start of the question.

(i) The reaction between 2-chlorobutane and hydroxide ions.

.. (2)

(ii) The reaction between ethanol and acidified potassium dichromate solution.

.. (1)

(d) A catalyst is used in the industrial manufacture of sulphuric acid. Justify the economic benefits of using a catalyst in terms of:

(i) the equilibrium involved;

..

..

..

.. (2)

(ii) the kinetics of the reaction.


..

..

..

.. (2)

(Total 13 marks)

34. (a) Potassium hydroxide can be used in substitution reactions with halogenoalkanes.

(i) 2-bromo-2-methyl propane is known to react with hydroxide ions via an SN1 mechanism. Give the rate equation for this reaction, and justify it by giving the mechanism and explaining the relationship between the rate equation and the mechanism. What is the role of the hydroxide ions in this reaction?

(6)

(ii) The halogenoalkane could contain chlorine, bromine, or iodine. Explain what effect, if any, the nature of the halogen has on the rate of the reaction.

(2)

(b) Potassium hydroxide is used for elimination reactions of halogenoalkanes. 2-Bromobutane gives two organic products when reacted with potassium hydroxide in ethanol, one of these having two stereoisomers. Give structural formulae for all three product molecules and explain the existence of the stereoisomeric forms in terms of the orbitals involved. What is the role of the hydroxide ions in this reaction?

(6)

(c) Tristearin is an ester found in animal fats, especially beef tallow, which can be hydrolysed by potassium hydroxide. Write an equation to represent the reaction, and state the importance of the potassium-containing product.

(4)

C H COOCH

C H COOCH

C H COOCH

17

17

17

35 2

2

35

35

Tristearin (Total 18 marks)

35. Alkenes undergo electrophilic addition whereas arenes, such as benzene, undergo electrophilic substitution.

(a) What is an electrophile?

.................................................................................................................................... (1)


(b) Propene, CH3CH==CH2, reacts with HBr to give CH3CHBrCH3 as the major product.

(i) What is the name of the compound CH3CHBrCH3?

............................................................................................................................ (1)

(ii) Give the mechanism for the reaction.

(3)

(iii) Explain why the major product is CH3CHBrCH3 rather than CH3CH2CH2Br.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................ (2)

(c) Benzene C6H6 reacts with CH3Br to give C6H5CH3.

(i) What catalyst may be used in this reaction?

............................................................................................................................ (1)

(ii) Give the mechanism for the reaction. You should include the step that forms the electrophile.

(4)


(d) Explain in terms of structure and bonding why benzene and propene react differently with

electrophiles.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (4)

(Total 16 marks)

36. (a) (i) Explain what is meant by the following terms.

Rate of reaction

.......

.......

Overall order of a reaction ................................................................................

.......

....... (2)

(ii) Explain why the order of reaction cannot be deduced from the stoichiometric equation for a reaction.

.......

.......

....... (1)


(b) Substitution reactions of halogenoalkanes, can proceed via an SN1 or SN2 mechanism.

When 1-bromobutane, CH3CH2CH2CH2Br, 2-bromobutane, CH3CH2CHBrCH3, and 2-bromo-2-methylpropane, (CH3)3CBr, are reacted separately with aqueous sodium hydroxide solution each gives the corresponding alcohol.

(i) Give the mechanism for the SN1 reaction between 2-bromobutane and hydroxide ions.

(3)

(ii) Explain why the product mixture is not optically active.

.......

.......

....... (2)

(iii) In an experiment designed to find the mechanism of the reaction between 2-bromo-2-methylpropane and hydroxide ions the following data were obtained at constant temperature.

Initial concentration of 2-bromo-2-methylpropane

/mol dm3

Initial concentration ofOH / mol dm3

Initial rate of reaction /mol dm3 s1

0.10 0.10 1.2 102

0.20 0.10 2.4 102

0.30 0.20 3.6 102

Use the data to deduce the rate equation for the reaction of 2-bromo-2- methylpropane with sodium hydroxide solution.

.......

.......

....... (3)


(c) Suggest, in outline, a method you could use to follow the progress of the reaction between

a bromoalkane and aqueous sodium hydroxide.

.......

.......

.......

.......

.......

....... (3)

(Total 14 marks)

37. (a) Benzene, C6H6, reacts with ethanoyl chloride, CH3COCl, to give a compound of molecular formula C8H8O.

(i) Identify another substance that must be present for this reaction to occur and state the function of this substance in this reaction.

.......

....... (2)

(ii) Give the mechanism for this reaction.

(4)


(b) Phenol, C6H5OH, reacts differently from benzene with ethanoyl chloride. State the type of

reaction that would occur between phenol and ethanoyl chloride and give the structure of the organic product.

Type of reaction ..

Structure of the organic product

(2)

(c) A benzene ring containing two hydroxy groups, C6H4(OH)2, can exist as a range of isomers.

(i) Draw the structure of each isomer.

(2)

(ii) A polymer can be formed by reacting one of these isomers with the di-acyl chloride, ClCOCH2COCl.

Draw a diagram indicating clearly the structure of such a polymer.

(2)


(d) The compound 4-hydroxyazobenzene

N N OH

can be obtained from phenylamine and phenol in two steps. Identify the intermediate formed and give the reagents and conditions for each step.

.........

.........

.........

.........

.........

......... (4)

(Total 16 marks)

38. (a) Alkenes such as ethene will take part in homolytic, free radical addition reactions to form polymers such as poly(ethene).

(i) Define the terms homolytic and free radical. (2)

(ii) Draw a repeating unit of the polymer that would be made by the same mechanism from phenylethene, C6H5CH=CH2.

(2)

(iii) Outline the difficulties involved in the disposal of polymers such as poly(phenylethene) by combustion and by landfill.

(2)

(iv) State a property of poly(phenylethene) and suggest why this makes it particularly useful.

(2)

(b) Ethene, C2H4, reacts with concentrated sulphuric acid by electrophilic addition of H+ and HSO4 across the double bond to give CH3CH2OSO3H.

(i) Suggest a mechanism for this electrophilic addition reaction. (3)

(ii) Describe a simple chemical test to confirm that the carbon-carbon double bond is not present in the product.

(2)

(c) (i) Use the concepts of the different types of covalent bonds and bond enthalpy to explain the structure of the benzene ring.

(5)


(ii) Explain why benzene normally reacts by electrophilic substitution rather than by

electrophilic addition. (2)

(d) Outline how a sample of pure benzene, C6H6 (boiling temperature 80 C), could be converted to a pure sample of nitrobenzene, C6H5NO2, (boiling temperature 211 C). Include in your answer the reagents and conditions involved and the technique for obtaining a sample of pure nitrobenzene from the reaction mixture.


39. (a) Benzene can be converted into nitrobenzene.

(i) Give the reagents for the reaction.

......................................................................................................................

...................................................................................................................... (2)

(ii) Write the mechanism for the reaction, including the formation of the species that attacks the benzene molecule.

(4)

(iii) Name the type of mechanism involved in this reaction.

...................................................................................................................... (1)


(b) Further reaction produces trinitrobenzene. Draw the structural formulae of the three

isomeric trinitrobenzenes.

(3)

(c) Give the reagents and conditions required for the conversion of nitrobenzene into phenylamine, C6H5NH2.

...............................................................................................................................

............................................................................................................................... (2)

(d) (i) Draw the structural formula of the organic product of the reaction between phenylamine and ethanoyl chloride, CH3COCl.

(1)


(ii) The organic product of the reaction in (d) (i) is a solid at room temperature.

An impure sample of the solid can be purified by recrystallisation. Describe how this recrystallisation can be carried out.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

...................................................................................................................... (6)

(Total 19 marks)

40. Consider the reaction scheme shown below, which starts with phenylethene.

C H CH CH C H Br C H OHA B

C

(i) KMnO / NaOH heat

(ii) HCl(aq)

C H O

6

6 27

5 2 8

4

89 9HBr

(a) (i) State the conditions under which hydrogen bromide could react with phenylethene. Give the structural formula of the major product.

.....................................................................................................................................

..................................................................................................................................... (3)


(ii) Give the mechanism for the reaction of hydrogen bromide with phenylethene. You

may represent phenylethene as RCH==CH2.

(3)

(iii) State why one isomer is the major product in the reaction in (i).

.....................................................................................................................................

..................................................................................................................................... (1)

(b) B is a secondary alcohol.

(i) What type of reaction is occurring in the conversion of A to B?

..................................................................................................................................... (1)

(ii) Give the structural formula for C.

(1)

(iii) In the production of C from B, acidification of the reaction mixture is needed. Why is this?

.....................................................................................................................................

..................................................................................................................................... (1)

(Total 10 marks)


41. (a) Chlorine can be produced by the electrolysis of concentrated sodium chloride solution,

brine, in a membrane cell.

(i) Give the half-equations for the processes that occur at the anode and at the cathode of the electrolytic cell. Name the other important product from this process.

(3)

(ii) Use the equations and the E values below to predict what happens if chlorine and aqueous sodium hydroxide solution are mixed, and write the overall ionic equation for the reaction.

E/V

Cl2 + 2e 2Cl +1.36

OCl + H2O + 2e Cl + 2OH +0.89 (3)

(iii) Name and explain the type of reaction occurring in (ii). (2)

(b) The most common chlorine-containing polymer is poly(chloroethene), usually known as PVC.

(i) Suggest the mechanism for the polymerisation of chloroethene, CH2==CHCl, to give PVC using an initiator that you may represent as the free radical R. Write enough of the mechanism to give a four-carbon chain, and show a termination step.

(4)

(ii) Most PVC is used for durable products, but some is waste. Suggest a use for PVC and comment on the difficulties that might arise from the disposal of PVC in landfill sites and by incineration.

(4)


(c) The chlorination of ethane in ultra-violet light has a free radical chain mechanism. The

first step is:

Cl2 2Cl The next step could be either:

CH3CH3 + Cl CH3CH2Cl + H (step I) or

CH3CH3 + Cl CH3CH2 + HCl (step II) Use the mean bond enthalpy data given below to show which of these two steps, I or II, is

the more likely.

Bond enthalpy /kJ mol1 CH +413 CCl +346 HCl +432


42. Aluminium chloride can be obtained in two forms: anhydrous, often represented as AlCl3, and a hydrate, AlCl3.6H2O.

(a) If anhydrous aluminium chloride is heated it sublimes at 185 C. In a closed vessel the gas is an equilibrium mixture of substances with molecular formulae AlCl3 and Al2Cl6.

Al2Cl6(g) 2AlCl3(g)

(i) At a given temperature a vessel of volume 10.0 dm3 contained initially 2.0 moles of Al2Cl6. When equilibrium was achieved 0.50 mol of Al2Cl6 remained.

Write an expression for Kc for the equilibrium and calculate its value under the stated conditions.

(4)

(ii) Draw a three-dimensional diagram of the Al2Cl6 molecule. Indicate the nature of the bonds on the diagram.

(3)


(b) Anhydrous aluminium chloride is used as a catalyst in Friedel-Crafts reactions, such as

that between benzene and chloroethane.

(i) Write the overall equation for this reaction. (1)

(ii) Give the mechanism for the reaction, including the formation of the electrophile. (4)

(iii) By comparing the bonding in ethene and in benzene, explain why ethene usually undergoes addition reactions whereas benzene usually undergoes substitution reactions.

(3)

(c) (i) Suggest why heating hydrated aluminium chloride gives hydrogen chloride gas, and identify the residue.

(2)

(ii) Dissolving the hydrate in water does not cause liberation of HCI gas but gives an acidic solution. Explain why the solution is acidic.


43. (a) The enthalpy of hydrogenation of cyclohexene is 120 kJ mol1.

+ H 2

(i) Predict the value of H for the reaction:

+ 2H 2

..................................................................................................................................... (1)

(ii) Suggest the value of H for the hydrogenation of the hypothetical molecule 1,3,5-cyclohexatriene:

+ 3H 2

..................................................................................................................................... (1)


(iii) The enthalpy of hydrogenation of benzene is 208 kJ mol1. Explain in terms of the

structure and bonding in benzene why this value is different from your answer to (a)(ii).

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (3)

(b) Benzene, C6H6, reacts with bromine to form bromobenzene, C6H5Br, and hydrogen bromide.

(i) Give the formula of the catalyst that is needed for the reaction.

..................................................................................................................................... (1)

(ii) Give the mechanism for the reaction, making clear the role of the catalyst.

(4)

(iii) State the type of mechanism that is commonly found with reactions of benzene and its derivatives.

..................................................................................................................................... (1)


(c) (i) Bromobenzene can be used to make the Grignard reagent C6H5MgBr.

How would C6H5MgBr be converted into 1-phenylethanol?

C

H

OH

C H6 5 CH3

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(ii) Benzene can also be converted into 1-phenylethanol by a different two-step synthesis. State the reagents and conditions needed for each of these steps.

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organic chemisty_reaction mechanisms

Documents

sn1 reaction

chiral halogenoalkane

chiral product

chiral compound

initial ratemol

case of sn1

sn2 mechanism

aqueous hydroxide ions