as 91391 describe aspects of organic chemistry collated polymer questions - polyesters ... ·...

No Brain Too Small CHEMISTRY AS 91391

AS 91391 Describe aspects of organic chemistry

COLLATED POLYMER QUESTIONS - polyesters, polyamides and peptides

(2018:2)

(b) Dipeptides are made from two amino acids joined by an amide (peptide) bond. The dipeptide shown below is made from glycine and alanine:

(i) Circle the amide (peptide) bond.

(ii) Compare and contrast the acidic and basic hydrolysis of the above dipeptide. Your answer should include:

• an explanation of the hydrolysis reaction

• structural formulae of the products formed when the dipeptide undergoes acidic and basic hydrolysis.

(2018:3)

Glycolic acid can be used to make polyglycolic acid (PGA), a polyester used to make dissolvable stitches. The structure of glycolic acid is shown below:

HO – CH2 – COOH

(a) (i) Draw a section of the PGA polymer chain to show THREE repeating units.

(ii) Identify and explain the type of reaction occurring in the formation of PGA.

(2017:3)

Peptides are molecules that form when amino acids combine. The following structures show the amino acids cysteine and serine.

(a) (i) Show two possible dipeptides that can be formed by combining the two amino acids shown

above.

(ii) Circle the amide functional group on ONE of the dipeptides drawn in part (i)


(b) Nomex® is a polymer used in firefighters’ suits. Nomex® is made up of two different monomers bonded together to form the polymer chain. A small portion of the structure of Nomex® is shown below.

Explain the structure of the polymer, Nomex®. In your answer, you should include: • the name of the functional group linking the monomers • a drawing of both monomers • a classification of the type of polymer formed, with an explanation to justify your choice.

(c) Polymers such as Nomex® can be hydrolysed by either aqueous acid or base. Show the products of the hydrolysis of Nomex® using: (i) aqueous acid (ii) aqueous base

(2016:1)

(a) Glycine, alanine, and serine are three amino acids shown below.

(iii) Draw the two possible dipeptides formed from the amino acids glycine and alanine.

(iv) Name the type of reaction that occurred when the dipeptides formed in (iii) above. Explain your choice.

(v) Draw the products of an acidic hydrolysis for ONE of the dipeptides from (iii) above. Explain why these products are formed.


(2015:2)

(c) A form of the polymer nylon can be made from the two monomers below.

(i) Draw the repeating unit of the polymer formed if these two monomers are used.

Consider the formation of this form of nylon in a laboratory.

(ii) Describe the type of reaction occurring and explain why this reaction results in a polymer.

(iii) Explain why sebacoyl chloride is dissolved in a non-polar organic solvent rather than in water.

(iv) Elaborate on the reaction that will occur if a dilute aqueous solution of acid is mixed with the newly formed polymer.

(2014:3)

(b) The following polymer will, under the correct conditions, hydrolyse.

(i) Draw the monomer(s) from which this polymer is formed.

(ii) Discuss the hydrolysis of the polymer. In your answer you should include:

• the conditions under which it can be hydrolysed • structures of the organic products formed as a result of hydrolysis.

(2013:3)

(d) Peptides are formed when amino acids combine.

(i) Show two possible dipeptides that can be formed by combining the amino acids:

(ii) Circle the amide link in each dipeptide.


From expired AS 90698

(2012:4 )

The structures of Polymer A and Polymer B are given below.

Polymer A

Polymer B

(a) Identify the monomers from which these polymers are made. (b) One of the polymers from above can be hydrolysed using NaOH(aq). Identify the polymer and draw

structures for the organic products of the hydrolysis. (c) Nylon 6,10 can be made from the monomers below.

Steps for the formation of Nylon 6,10 are given below: 1. 2 g of the diamine is dissolved in 25 mL of water. 2. 2.5 mL of sebacoyl chloride is dissolved in 25 mL of a non-polar organic solvent. 3. The dissolved sebacoyl chloride is poured into the diamine solution. 4. 5 g of NaHCO3 is added. 5. The nylon is extracted from the interface between the diamine and sebacoyl chloride layers. • Identify the repeating unit of the polymer formed. • Explain why the diamine is water soluble. • Explain why the sebacoyl chloride is dissolved in a non-polar organic solvent. • Explain why NaHCO3 is added.

(2011:2)

Nylon 6,6 is a polymer with the following structure:

(a) Circle an amide linkage in the structure above.


(b) Draw TWO monomers that could have formed this polymer.

(c) Nylon 6 is formed from the monomer H2N – (CH2)5 – CO2H.

(i) Name this monomer.

(ii) Draw THREE repeating units of the Nylon 6 polymer chain.

(d) Nylon is used for making ropes for climbing and abseiling. The ropes come with a warning label attached, such as that shown below.

Discuss why this warning label is attached to nylon rope when purchased. Include in your answer: • the type of reaction that would occur • relevant organic structural formulae • any changes to the properties of the nylon rope

(2010:3)

The polymer commonly known as Kevlar is used to make bullet-proof vests and bicycle tyres. It can be made in a condensation reaction from either of the following pairs of monomers:

However, the second pair of monomers needs to be heated for the polymerisation reaction to take place.

Note: is a benzene ring and should be treated as a hydrocarbon chain. It is not a functional group and does not change during the reaction.

Discuss these polymerisation reactions.

Your answer should include:

• a repeating unit of the polymer chain • reasons for the choice of monomers • identification of the functional group in the polymer • a reason why this is classified as a condensation reaction • a comparison of the two pairs of monomers, including the reason that the second reaction will not

take place without heating.

WARNING!!!

Nylon Rope: Do not allow to come in contact with acids or their vapours


(2009:3)

(a) Kodel is a polymer with the following structure:

(i) Identify TWO monomers for this structure. (ii) Explain why this type of polymer is known as a condensation polymer.

(b) Compound X is a polymer which can be hydrolysed to give a single monomer, Compound Y, which has the molecular formula C3H6O3.

Compound Y will turn blue litmus red, and can exist as enantiomers (optical isomers). It will react with acidified potassium dichromate to form Compound Z, which has the molecular formula C3H4O3.

Compound Z does not react with Tollens’ reagent.

(i) Draw the structures of Compounds Y and Z. (ii) Draw a section of the polymer, Compound X, showing at least two repeating units.

(2008:2)

Amino acids are the building blocks that make up proteins. Alanine and valine are amino acids which can combine to form dipeptides.

C

H

H

H C

H

N

H

H

C

O

OH

C

H

H

H C

H

CH H

H

C

H

N

H

H

C

O

OH

alanine valine

Draw the structure of a possible dipeptide formed from the combination of alanine and valine.

(2007:2)

(c) Lactic acid is able to form a condensation polymer in the presence of dilute sulfuric acid.

Draw three repeating units of this polymer.

Monomer:


(2006:2)

Draw a single repeating unit for the nylon polymer formed.

(2005:2)

(b) Polyesters are polymers that can be made from two different monomers or from a single monomer.

Discuss this statement, using the structures of specific monomers and the polyesters that can be made from them, to illustrate your answer. Your answer should demonstrate a clear understanding of the highlighted terms.

(2004:1)

(e)

undergoes a condensation reaction with the following molecule

(commonly referred to as alanine).

It forms two different organic products referred to as dipeptides.

(i) Draw the structural formulae for the two possible dipeptides. (ii) Explain why the formation of dipeptides is referred to as a ‘condensation reaction’.


Answers (2018:2)

(b) (i) Circle around HN–C=O group. Water is used to break the amide (peptide) bond. H is added to one molecule and OH to the other. The NH2 group gains a proton (H+) in acidic conditions / forms NH3+. The COOH group loses a proton (H+) in basic conditions / forms COO–. Acidic conditions:

Basic conditions:

(2017:3)

(d) (i) Second dipeptide the same structure above, with the CH2SH swapped with CH2OH.

(ii) Amide linkage group circled on one of the dipeptides (e) Nomex® has an amide linkage – see (a)(ii) above.

Monomers:

This is a condensation polymer / polyamide, as monomers join / amide link forms and a molecule of water or HCl is released during the reaction.


(c) (i) (ii) Two forms of hydrolysis:

(2016:1)

(c) (iii) Dipeptides:

(vi) Condensation. Two larger molecules are joined together with the elimination of a smaller

molecule. (v) Acidic hydrolysis leaves COOH group intact and NH2 group becomes protonated to form NH3+.

H3N+ CH(CH3)COOH H3N+CH2COOH


(2015:2)

(c) (i)

(ii) This is condensation or substitution (polymerisation), whereby the two monomers are joined together and a small molecule (HCl(g)) is released. Each monomer is di-functional or has a reactive site at each end (allowing polymerisation to be ongoing.)

(iii) The sebacoyl chloride (as an acyl chloride) reacts vigorously with water forming the carboxylic acid, (however, it does not react with the nonpolar solvent.)

(iv) Dilute acid will cause hydrolysis of the amide linkage. The products formed would be (di)ammonium salt or +H3N(CH2)6NH3+ and the (di)oic acid. HOOC(CH2)8COOH (Names not required)

(2014:3)

(b) (i) (ii) Acid hydrolysis conditions: H2O/H+ or HCl(aq) and heat or reflux

Basic hydrolysis conditions: H2O/OH¯ or NaOH(aq) and heat or reflux

(2013:3)

(d) (i) & (ii) TWO correct structures drawn and amide linkages identified with circles.


From expired AS 90698 – but still relevant

(2012:4)

(a) Monomers of Polymer A:

Monomer of Polymer B: H3C-CH2-CH=CH2

(b) Polymer A HOCH2CH2OH AND Na+ – OOCCH2COO– +Na OR – OOCCH2COO– OR NaOOCCH2COONa (c) The diamine is water soluble because it is a polar molecule / forms hydrogen bonds with water /

partially ionises. Sebacoyl chloride (acid chloride) is dissolved in the non-polar solvent, as it reacts (vigorously) with water forming acidic solutions. NaHCO3 is added to the solution to neutralise the HCl / neutralise the acid formed during the reaction / prevent the nylon from undergoing acid hydrolysis.

(2011:2)

(a) One link is circled. (b) One set of monomers (can be in any order)

(c) (i) 6-amino hexanoic acid

(ii)

(d) The acid would hydrolyse the rope. This would cause the amide linkages to break and form the monomers. The rope would lose strength.

OR products from nylon 6,6.


(2010:3)

The repeating group is:

• The monomers have functional groups at both ends, so can react to form a long chain. (mention of

diacid chloride, diacid, diamine sufficent). • The acid chloride and amine react to give an amide functional group or peptide bond. • The reaction is a condensation reaction, since a small molecule (HCl or H2O) is released. • When the amine and the acid are used without heating, a proton transfer (acid-base reaction) occurs

and hence polymerisation does not occur until the reaction is heated. • The acid chloride is more reactive than the carboxylic acid.

Additional explanation

C

O

Cl

C

O

Cl

NH

H

N

H

H

diacyl chloride diamine

No heat is needed since the –COCl group is so much more reactive than the –COOH group.

NH

H

NH

C

O

C

O

Cl

amide/peptide link

This is of course just a small section of the polymer as further units would react in an ABABABA fashion……


NH

H

N

H

H NH

H

NH

C

O

C

O

Cl

C

O

OH

C

O

OH

NH

H

N

H

H

will give the same polymer but this reaction needs heat otherwise will just be an acid-base reaction between –COOH (acid) and –NH2 (base) functional groups.

(2009:3)

(a) (i)

H O C

H

H

C

H

H

O H

and

either

C

O

Cl

C

O

Cl

OR

C

O

OH

C

O

OH

(ii) A small molecule, such as H2O or HCl, is eliminated when the monomers join.

No Brain Too Small CHEMISTRY AS 91391 Additional explanation Find the repeating units – and where the monomers joined to make the polymer – the ester link is the key to this question. “Break up” the structure where it would have formed in an esterification reaction. And remember there are 2 ways to make an ester:

R-COOH + HO-R or R-COCl + HO-R

(b)

(i) Compound Y has the molecular formula C3H6O3.

Compound Y will turn blue litmus red – it must be an acid with a –COOH group

Can exist as enantiomers (optical isomers) – it must have a chiral / asymmetric carbon atom

It will react with acidified potassium dichromate to form Compound Z with a molecular formula C3H4O3 – it must have a 1o or 2o alcohol group or an aldehyde group to be able to be oxidised by the acidified potassium dichromate; the only one that could give you the chiral C is if it is a 2o alcohol.

Compound Z, C3H4O3, does not react with Tollens’ reagent – It must still have the –COOH group and since it is NOT an aldehyde, it must have a ketone group and so Y must have had a 2o alcohol group.

Y: Z:

C

H

H

H C

H

O

H

C

O

OH

CH

H

H

C

O

C

O

OH

So put the 2 x -H back onto the -O and O- to give 2 x –OH alcohol groups…

So put the H’s back onto the -O and O- to give 2 x –OH alcohol groups…

So put the 2 x -OH back onto the C=O to give 2 x –COOH carboxylic acid groups…

OR 2 x –Cl back onto the C=O to give 2 x –COCl acyl (acid) chloride groups

So put the 2 x -OH back onto the C=O to give 2 x –COOH carboxylic acid groups…

OR 2 x –Cl back onto the C=O to give 2 x –COCl acyl (acid) chloride groups

ester link


(iii) Section of the polymer, Compound X, showing at least two repeating units. Z has –OH and –COOH on the same molecule so could form a polymer with an ester link

C

H

H

H C

H

O

H

C

O

OH

can be redrawn as

C HH

H

C

H

OH C

O

OH

C HH

H

C

H

OH C

O

OH

C HH

H

C

H

OH C

O

OH

C HH

H

C

H

OH C

O

OH

to give ( + water molecules) (2008:2)

Amino acids are the building blocks that make up proteins. Alanine and valine are amino acids which can combine to form dipeptides.

or

Additional explanation Redraw each monomer so H2N-X-COOH and H2N-Y-COOH then lose a molecule of water from –OH of –COOH on one molecule and –H of H2N- of other, forming an amide link.

NOTE: Because the two amino acids were different you can form 2 different dipeptides; 2! (2x1).


They are different because has valine as the N-terminus (NH2 end) and

alanine as the C-terminus, while has alanine as the N-terminus and valine as the C-terminus.

(If there were 3 different amino acids you could form 6 different tripeptides - 3! (3x2x1).

(2007:2)

(c)

(needs 3 units and correct “ends”) Additional explanation

H O C

H

C HH

H

C

O

OH

H O C

H

C HH

H

C

O

OH

H O C

H

C HH

H

C

O

OH

(2006:2)

Repeating unit is an amide linkage, ie

–HN(CH2)6NHOC(CH2)4CO–

(dimer acceptable)

Or

N

H

HC

H

HC

H

HC

H

HC

H

HC

H

HC

H

HN

H

C

OC

H

H

C

H

H

C

H

H

C

H

H

C

O

OH


(2005:3)

• A polymer is a long chain molecule formed when many molecules or units (ie monomers) link together. • Polyester chains are formed by condensation with the loss of H2O or HCl at each ester linkage.

• Polyesters contain ester linkages. • A single monomer must be a hydroxyl alkanoic acid or hydroxy alkanoyl chloride eg HO(CH2)4COOH /

HO-R-COOH (could just say must have an alcohol and a carboxylic acid / acyl chloride functional group on it).

• Two different monomers can be a diol and a dioic acid / a diol and a dioyl chloride

HOOC(CH2)nCOOH + HO(CH2)mOH

ClOC(CH2)nCOCl + HO(CH2)mOH

Or two different hydroxy alkanoic acids / two different hydroxy alkanoyl chlorides eg

HOOC(CH2)nOH + HOOC(CH2)mOH

ClOC(CH2)nOH + ClOC(CH2)mOH

(2004:1)

(e)

(i)

(ii) Condensation reaction results in removal of a small molecule OR water during the bonding

reaction between the 2 molecules, in this case a water molecule is produced for every peptide bond formed. The OH is removed from the carboxylic acid group/end and the H is removed from the amine group/end.

as 91391 describe aspects of organic chemistry collated polymer questions - polyesters ... ·...

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