NT Exampro 1

1. (a) 2-aminobutane, CH3CH2CH(NH2)CH3, is a chiral molecule that can be optically active. It

can be made from CH3CH2CH(CONH2)CH3.

(i) What is a chiral molecule?

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

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

(ii) How is optical activity detected experimentally?

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

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

(b) State the reagents and conditions necessary to convert CH3CH2CH(CONH2)CH3

to 2-aminobutane.

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

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

(c) (i) CH3CH2CH(CONH2)CH3, D, can be made from 2-bromobutane in four steps

shown below.

CH CH CHBrCH Grignard A B

PCL

CH CH C CH C

CONH

H

2

2

3

3 32

2

5

3

D

Mgi) COii) HCl(aq)

NT Exampro 2

Give the structural formulae of the three intermediate compounds A, B and C.

A

B

C

(3)

(ii) Grignard reagents are often made in a solvent of dry ethoxyethane. Why must the

ethoxyethane be dry?

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

(iii) Give the reagents and conditions for the conversion of C to D.

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

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

(d) Butanone can be made from 2-bromobutane by a synthetic route involving two steps, the

first using aqueous sodium hydroxide and the second potassium dichromate(VI) solution

acidified with dilute sulphuric acid.

(i) Give the structural formula of the intermediate compound in this synthetic route.

(1)

NT Exampro 3

(ii) Butanone reacts with 2,4-dinitrophenylhydrazine solution but not with Fehling’s

solution. Why is this?

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

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

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

(iii) Butanone also reacts with iodine in sodium hydroxide solution. What structural

feature of butanone is shown by this reaction?

(1)

(iv) Give the structural formulae of both the organic products from the reaction in (iii).

(2)

(Total 17 marks)

2. (a) Three isomers A, B and B have the molecular formula C4H8O.

All three compounds give an orange precipitate with 2,4-dinitrophenylhydrazine reagent.

B and C also give a silver mirror when warmed with ammoniacal silver nitrate solution.

Write the structural formulae of A, B and C .

Substance A

NT Exampro 4

Substance B

Substance C

(3)

(b) Substance A reacts with the Grignard reagent, C2H5MgBr

(i) Give the equation for the preparation of this Grignard reagent.

….……………………………………………………………………………. (1)

(ii) State the conditions for this preparation.

….…………………………………………………………………………….

….……………………………………………………………………………. (2)

(iii) Write the structural formula of the product obtained when this Grignard reagent

reacts with substance A.

(1)

NT Exampro 5

(c) C2H5MgBr reacts with carbon dioxide to form the acid C2H5COOH. This acid can be

converted to propanamide in a two step process.

C2H5COOH

step 1

C2H5COCl

step 2

C2H5CONH2

State the reagent required for each step.

Step 1 ………………………………….

Step 2 …………………………………. (2)

(d) C2H5MgBr also reacts with ethanal to form substance D, which exists as a pair of optical

isomers.

(i) Draw the structural formulae of these two isomers and use them to explain why

these isomers exist.

(4)

(ii) What is the difference in property between these isomers?

….……………………………………………………………………………. (1)

(e) (i) Write down the name and the structural formula of the organic compound formed

when substance D is heated under reflux with a solution of potassium

dichromate(VI) in dilute sulphuric acid.

Name …………..……………………………………………………………

Structural formula.

(2)

(ii) State the colour of the solution remaining after this reaction.

….……………………………………………………………………………. (1)

(Total 17 marks)

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

NT Exampro 6

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

.................................................................................................................................... (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.

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

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

.......................................................................................................................... (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

–3–3 –Initial rate/mol dm s–3 –1

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

the reaction.

NT Exampro 7

(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)

4. Three compounds A, B and C have the molecular formula C4H8O. All three compounds give a

yellow precipitate with 2,4-dinitrophenylhydrazine reagent, B and C also give a silver mirror

with ammoniacal silver nitrate solution and a red precipitate with Fehling’s solutions.

(a) Suggest possible identities for the compounds A, B and C by completing the table below.

Structural formula Name

A

B

C

(6)

NT Exampro 8

(b) The reduction of A gives D, C4H10O.

(i) D exists as a pair of optical isomers. Draw a structural formula for D and use it to

explain why these isomers exist.

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

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

(ii) What is the difference in property between the isomers?

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

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

(iii) What class of compound is D?

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

(c) What class of compound is produced when B and C are reduced?

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

(d) Write down the name of the organic compound formed when substance B is heated with

acidified sodium dichromate(VI), and state the colour of the remaining solution.

Name: ..................................................................................................................

Colour: .................................................................................................................. (2)

(Total 15 marks)

5. (a) State the reagent(s) used for the conversion of ethanol to

(i) iodoethane

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

(ii) ethene

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

NT Exampro 9

(b) Suggest a series of reactions by which ethanol can be converted to 2-hydroxypropanoic

acid, CH3CH(OH)COOH. For each reaction specify the reagents and conditions

necessary.

(6)

(c) Explain whether a solution of 2-hydroxypropanoic acid, made in this way, would have

any effect on a beam of plane polarised monochromatic light.

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

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

(d) 2-hydroxypropanoic acid reacts with lithium tetrahydridoaluminate (III)(lithium

aluminium hydride).

State the conditions necessary for this reaction and give the structural formula of the

organic product.

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

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

Structural formula

(2)

(Total 12 marks)

NT Exampro 10

6. (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)

NT Exampro 11

(iv) Explain briefly, by reference to its structure, why ethene would not react with HCN

in a similar way.

…………………………………………………………………………………

………………………………………………………………………………… (1)

(Total 13 marks)

7. (a) State the reagents and the conditions required for:

(i) the elimination of HBr from 2-bromopropane;

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

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

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

(ii) the reduction of butanoic acid to butan-1ol;

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

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

(iii) the conversion of animal fat into soap.

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

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

(b) Give the functional group identified by a positive test with each of the following reagents.

2,4 dinitrophenylhydrazine reagent: ..........................................................................

Ammoniacal silver nitrate: .........................................................................................

Phosphorus pentachloride: .........................................................................................

Bromine water: ........................................................................................................... (4)

(c) Three compounds P,Q and R all have the same molecular formula C4H8O.

When 2,4-dinitrophenylhydrazine reagent was added to each, P gave a precipitate.

When ammoniacal silver nitrate was warmed with each, P gave a silver mirror.

When phosphorus pentachloride, PCl5, was added to dry samples of each, Q and R gave

off steamy fumes.

When bromine water was shaken with each, Q and R turned it colourless.

(i) Draw two possible structural formulae for P.

NT Exampro 12

(2)

(ii) Q is chiral and can be oxidised to a ketone. Draw the structures to show the two

optical isomers of Q.

(2)

(iii) R can be oxidised to an acid S which has geometric isomers. Draw the formula of

the two geometric isomers of the acid S.

(2)

(Total 17 marks)

8. Citral is a colourless natural product, which gives lemons their characteristic flavour and smell.

Its structural formula is:

C C

CH CH

CH CH CHO

3 3

CH 3 CH CH2 2

(a) (i) How would you show that citral has a carbonyl group, C==O?

Reagent .....…………………………………………………………….………

Observation ………………………………………..………………………….. (2)

(ii) How would you show that citral is an aldehyde?

Reagent .....…………………………………………………………….………

Observation ………………………………………..………………………….. (2)

NT Exampro 13

(b) Citral has geometric isomers. Draw them and explain why they are not easily

interconvertable.

Structures:

Reason

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

(c) Bromine, dissolved in tetrachloromethane, was added slowly to a solution of citral.

(i) Describe what you would observe when this was done.

…..……………………………………………………………………………..

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

(ii) Draw the structural formula of the product of this reaction when excess bromine

is added.

(1)

(iii) This product is chiral. Mark all the atoms which cause chirality with a ∗ on the

structural formula that you have given in (ii) above. (2)

NT Exampro 14

(d) Citral can be reduced to an alcohol

(i) State a reagent and the conditions that could be used for this reaction.

Reagent .....…………………………………………………………….………

Conditions ………………………………………..…………………………… (2)

(ii) How would you test the product to show that it has an ––OH group?

Reagent .....…………………………………………………………….………

Observation ………………………………………..………………………….. (2)

(e) Citral can be oxidised to an acid C9H15COOH (Mr = 168) which ionises in water

C9H15COOH + H2O ⇔ H3O+ + C9H15COO–

4.62 g of this acid was dissolved in water to give a solution of volume 250 cm3.

This solution had a pH of 2.91.

(i) Write the expression for Ka for this acid.

(1)

(ii) Calculate the concentration of the acid in mol dm–3.

(1)

(iii) Calculate the value of Ka of the acid.

(3)

(Total 20 marks)

9. Propenal, CH2=CHCHO, is one of the materials that gives crispy bacon its sharp odour. In the

following question assume that the carbon–carbon double bond and the aldehyde group in

propenal behave independently.

NT Exampro 15

(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

H

C 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)