Amino Acids Past Paper Questions (2024)

Q1.

Proteins are polymers made from amino acids.

Part of the structure of a protein is shown.

–Cys–Ser–Asp–Phe–

Each amino acid in the protein is shown using the first three letters of its name.

(a) Identify the type of protein structure shown.

Tick (✓) one box.

(1)

(b) Draw a structure for the –Cys–Ser– section of the protein.

Use the Data Booklet to help you answer this question.

(2)

(c) Name the other substance formed when two amino acids react together to form part of a protein chain.

(1)

The general structure of an amino acid is shown.

R represents a group that varies between different amino acids.

R groups can interact and contribute to protein structure.

(d) Explain why the strength of the interaction between two cysteine R groups differs from the strength of the interaction between a serine R group and an aspartic acid R group.

Use the Data Booklet to help you answer this question.

(4)

(e) Deduce the type of interaction that occurs between a lysine R group and an aspartic acid R group.

(1)

(Total 9 marks)

Q1.

(a) Primary

1

(b)

OR

M1 for correct peptide link (Allow -CONH- as a minimum)

M1

M2 for the correct amino acid R groups

Dipeptide can only score M1

M2

Trailing bonds not needed

(c) Water

Allow H₂O

1

(d) Two Cys R groups form a disulfide bridge/link stated or described

Could score via a correct diagram showing min -SS-

M1

Ser and Asp R groups form Hydrogen bonds

Allow H bonds

M2

Disulfide bridges are stronger than H bonds

Interactions between cys R groups are stronger

M3

Because disulfide bridges are covalent bonds (while H bonds aren’t)

Because covalent bonds are stronger (than H bonds)

M4

(e) Ionic bond

1

[9]

Q2.

Which is the main species present in an aqueous solution of aspartic acid at pH = 14?

A
B
C
D

(Total 1 mark)

Q3.

Which compound is not a 2-aminocarboxylic acid?

(Total 1 mark)

Q4.

Which is the structure of a zwitterion of an amino acid?

A

B

C

D

(Total 1 mark)

Q5.

Which structure shows the zwitterion of an amino acid?

A
B
C
D

(Total 1 mark)

Q6.

Use the Data Booklet to help you answer this question

Which is the main aspartic acid species present in an aqueous solution at pH = 14?

A
B
C
D

(Total 1 mark)

Q2.

D

[1]

Q3.

B

CH₃CH(NH₂)CH₂COOH

[1]

Q4.

D

[1]

Q5.

D

[1]

Q7.

Use the Data Booklet to help you answer this question about amino acids.

The diagram shows parts of two polypeptide chains in a beta-pleated sheet of a protein.

(a)The polypeptide chains are held together by hydrogen bonding as shown in the diagram.

Explain how these hydrogen bonds form.

(2)

(b)A different type of bond can form between two polypeptide chains when the chains each contain the amino acid cysteine.

Complete the structure to show the bond that forms between the side chains of two cysteine molecules.

(1)

(c)The type of bond in part (b) between two polypeptide chains influences the three-dimensional structure of the protein.

Name this type of protein structure.

(1)

(d)Draw the structure of the zwitterion of a dipeptide formed by alanine and serine.

(2)

(Total 6 marks)

Q7.

(a)electron deficient H

Allow H delta plus / slightly positive

M1

(Which attracts) lone pair/electron pair on O

Penalise lone pair/electron pair donation

M2

(b)

Penalise dashed/dotted S—S

Ignore extra additions to structures

1

(c)Tertiary or Quaternary

Allow 3° or 4°

do not penalise minor error in spelling e.g. Quarternary

1

(d)

OR

Incorrect peptide bond CE=0

M1 for correct dipeptide

M2 for correct charges

Ignore additional dipeptide in working

Allow –CONH— or –COHN—

1

1

[6]

Q8.

Which structure is formed by aspartic acid in solution at pH 12?

A
B
C
D

(Total 1 mark)

Q9.

Use the Data Booklet to help you answer this question.

This question is about amino acids and peptide (amide) links.

(a)Draw the structure of the zwitterion formed by phenylalanine.

(1)

(b)Draw the structure of serine at high pH.

(1)

(c)Draw the structures of both dipeptides formed when phenylalanine reacts with serine.

In each structure show all the atoms and bonds in the amide link.

(2)

(d)An amide link is also formed when an acyl chloride reacts with a primary amine.

Name and outline a mechanism for the reaction between CH₃CH₂COCl and CH₃CH₂NH₂

Give the IUPAC name of the organic product.

(6)

(Total 10 marks)

Q8.

D

[1]

Q9.

(a)

Allow −CO₂⁻

Allow ⁺H₃N− and NH₃⁺−

1

(b)

(c)

1

1

If same wrong amino acid twice – max 1

(d)(nucleophilic) addition-elimination

Not electrophilic addition-elimination.

M1

M2 for arrow from lp on N to C

(or to space half way between N and C)

Ignore δ+ and δ− unless wrong

M3 for arrow from C=O bond to O

Not score M3 as an independent first step, but can allow M2 for attack on C+ produced

If Cl lost at this stage, Max 1 for mechanism for M2

M4 for structure of ion including 2 charges

(+ on N must be correct in both cases if drawn twice)

M5 for 3 arrows and lp on O

– may be scored in two steps

Ignore use of RNH₂ to remove H⁺ in M5, but penalise use of Cl⁻

M2-5

N-ethylpropanamide

M6

[10]

Q10.

Which structure shows 2-aminobutanoic acid as a zwitterion?

A
B
C
D

(Total 1 mark)

Q11.

The tripeptide shown in the following figure is formed from the amino acids glycine, threonine and lysine.

(a) Draw a separate circle around each of the asymmetric carbon atoms in the tripeptide in the figure.

(1)

(b) Draw the zwitterion of glycine.

(1)

(c) Draw the structure of the species formed when glycine reacts with an excess of bromomethane.

(1)

(d) Deduce the IUPAC name of threonine.

(1)

(e) Draw the structure of the species formed by lysine at low pH.

(1)

(Total 5 marks)

Q10.

B

[1]

Q11.

(a)

1

(b)

1

(c)

Allow

1

(d) 2-amino-3-hydroxybutanoic acid

1

(e)

1

[5]

Q12.

Proteins contain sequences of amino acids joined by peptide links.

Amino acid chains (polypeptides) are attracted to each other by hydrogen bonding.

(a) (i) A section of a protein is formed from one molecule of each of the amino acids glycine (H₂NCH₂COOH) and alanine (H₂NCH(CH₃)COOH).

Add bonds and atoms to the diagram to complete a structural formula for this section of the protein.

(2)

(ii) Draw a diagram to show how an amino acid chain can form a hydrogen bond with another amino acid chain.

Your diagram need only show the relevant atoms from one amino acid in each chain.

(1)

(b) Leucine, serine and glutamic acid are naturally-occurring amino acids.

(i) Give the IUPAC name of leucine.

(1)

(ii) Draw the structure of the zwitterion of serine.

(1)

(iii) Draw the structure of the ester formed by two molecules of serine.

(1)

(iv) Draw the structure of the species formed by glutamic acid at low pH.

(1)

(Total 7 marks)

Q12.

(a) (i)

Only one molecule of each used

M1 for 2 amide links

M2 CH₂ and CH(CH₃)

Allow 1 mark after one error

Dipeptide max 1

Treat both trailing bonds missing as one error

Ignore n

2

(ii)

No need to show lp

The covalent bond and the hydrogen bond either side of the H must be linear.

1

(b) (i) 2-amino-4-methylpentan(-1-)oic acid

Ignore hyphens, commas, spaces

1

(ii)

Allow -NH₃⁺

1

(iii)

1

(iv)

Allow -NH₃⁺

1

[7]

Q13.

A peptide is hydrolysed to form a solution containing a mixture of amino acids. This mixture is then analysed by silica gel thin-layer chromatography (TLC) using a toxic solvent. The individual amino acids are identified from their R_f values.

Part of the practical procedure is given below.

1.Wearing plastic gloves to hold a TLC plate, draw a pencil line 1.5 cm from the bottom of the plate.

2.Use a capillary tube to apply a very small drop of the solution of amino acids to the mid-point of the pencil line.

3.Allow the spot to dry completely.

4.In the developing tank, add the developing solvent to a depth of not more than 1 cm.

5.Place your TLC plate in the developing tank.

6.Allow the developing solvent to rise up the plate to the top.

7.Remove the plate and quickly mark the position of the solvent front with a pencil.

8.Allow the plate to dry in a fume cupboard.

(a) Parts of the procedure are in bold text.

For each of these parts, consider whether it is essential and justify your answer.

(4)

(b) Outline the steps needed to locate the positions of the amino acids on the TLC plate and to determine their R_f values.

(4)

(c) Explain why different amino acids have different R_f values.

(2)

(Total 10 marks)

Q13.

(a) Wear plastic gloves:

Essential – to prevent contamination from the hands to the plate

1

Add developing solvent to a depth of not more than 1 cm³:

Essential – if the solvent is too deep it will dissolve the mixture from the plate

1

Allow the solvent to rise up the plate to the top:

Not essential – the R_f value can be calculated if the solvent front does not reach the top of the plate

1

Allow the plate to dry in a fume cupboard:

Essential – the solvent is toxic

Allow hazardous

1

(b) Spray with developing agent or use UV

1

Measure distances from initial pencil line to the spots (x)

1

Measure distance from initial pencil line to solvent front line (y)

1

R_f value = x / y

1

(c) Amino acids have different polarities

1

Therefore, have different retention on the stationary phase or different solubility in the developing solvent

1

[10]

Q14.

(a) The structures and common names of two amino acids are shown.

(i)Draw the structure of the zwitterion of proline.

(1)

(ii)Draw the structure of the tripeptide formed when a proline molecule bonds to two alanine molecules, one on each side.

(2)

(b) Sections of two polymers, L and M, are shown.

(i)Give the IUPAC name of a monomer that forms polymer L.

(1)

(ii)Give the IUPAC name of the monomer that forms polymer M.

(1)

(iii)Draw the section of a polymer made from a dicarboxylic acid and a diamine that is isomeric with the section of polymer M shown.

(1)

(vi)Explain why polymer L is non-biodegradable.

(1)

(Total 7 marks)

Q14.

(a) (i)

Allow CO₂^– and NH₂⁺

1

(ii)NOTE − Two marks for this clip

M1 for alanine section bonded through N

M2 for alanine section bonded through C

But penalise error in proline ring

1

Allow MAX 1 for correct tripeptide in polymer structure

1

(b) (i)3-methylpent-2-ene

Ignore E-Z, commas, spaces or missing hyphens

1

(ii)4-amino-3-methylbutanoic acid

Ignore commas, spaces or missing hyphens

1

(iii)

or any polyamide section containing

8 carbons plus two C=O plus two N-H, such as

Trailing bonds are required

1

(iv)Non polar OR no polar groups / bonds (for attack by water / acids / alkalis / nucleophiles or for hydrolysis)

C-C bonds are strong

1

[7]

Q15.

Lysine and alanine are two amino acids.

(a) Give the IUPAC name of lysine.

(1)

(b) Draw structures to show the product formed in each case when lysine reacts with

(i)an excess of aqueous HCl

(1)

(ii)an excess of aqueous NaOH

(1)

(iii)methanol in the presence of a small amount of concentrated H₂SO₄

(1)

(c) The mass spectrum of alanine gives a major peak at m / z = 44

Write an equation for the fragmentation of the molecular ion of alanine to give an ion that produces this peak.
In your answer, draw the displayed formula for this fragment ion.

(2)

(d) Draw a dipeptide formed from one molecule of lysine and one molecule of alanine.

(1)

(e) The dipeptide in part (d) is hydrolysed in acid conditions and the mixture produced is analysed by column chromatography. The column is packed with a resin which acts as a polar stationary phase.

Suggest why lysine leaves the column after alanine.

(2)

(Total 9 marks)

Q15.

(a)2,6-diaminohexanoic acid

Ignore additional , or – or spaces.

1

(b)(i)

NB both N must be protonated.

Allow −NH₃⁺allow CO₂HAllow −⁺H₃N.

Penalise – C₄H₈ – here.

1

(ii)

Allow CO₂⁻.

Allow −H₂N.

Allow –COONa but penalise O–Na bond shown.

1

(iii)

Allow CO₂CH₃.

Allow −NH₃⁺ or –H₂N.

1

(c)

1 for displayed formula of fragment ion.

1 for molecular ion of alanine AND radical.

Allow molecular ion without brackets and fragment ion in brackets with outside +.

Allow dot anywhere on radical.

Allow [C₃H₇NO₂] for molecular ion.

2

(d)

OR

OR

Dipeptide, not repeating unit /.

Allow CO₂H Allow –H₂N.

Allow –CONH–.

1

(e) M1In acid lysine has double positive or more positive charge

1

M2(Lysine ion) has greater affinity / greater attraction / adheres better / sticks better to polar / stationary phase

M2 only scores after a correct M1.

Ignore greater retention time.

1

[9]

Q16.

Alanine and aspartic acid are naturally occurring amino acids.

(a) Draw the structure of the zwitterion formed by alanine.

(1)

(b) Draw the structure of the compound formed when alanine reacts with methanol in the presence of a small amount of concentrated sulfuric acid.

(1)

(c) Draw the structure of the species formed by aspartic acid at high pH.

(1)

(d) Draw the structure of a dipeptide formed by two aspartic acid molecules.

(1)

(Total 4 marks)

Q16.

(a)

Allow −NH₃⁺ and ⁺NH₃−

1

(b)

Allow protonated form, i.e. −NH₃⁺ or ⁺NH₃−

1

(c)

Allow – CO₂^–

1

(d)

Allow zwitterion with any COO⁻

Allow use of “wrong” COOH

1

[4]

Q17.

(a)The tripeptide shown is formed from the amino acids alanine, threonine and lysine.

(i)Draw a separate circle around each of the asymmetric carbon atoms in the tripeptide.

(1)

(ii)Draw the zwitterion of alanine.

(1)

(iii)Give the IUPAC name of threonine.

(1)

(iv)Draw the species formed by lysine at low pH.

(1)

(b) The repeating unit shown represents a polyester.

(i)Name this type of polymer.

(1)

(ii)Give the IUPAC name for the alcohol used to prepare this polyester.

(1)

(c) The repeating unit shown represents a polyalkene co-polymer. This co-polymer is made from two different alkene monomers.

(i)Name the type of polymerisation occurring in the formation of this co-polymer.

(1)

(ii)Draw the structure of each alkene monomer.

(2)

(d) One of the three compounds shown in parts (a), (b) and (c) cannot be broken down by hydrolysis.

Write the letter (a), (b) or (c) to identify this compound and explain why hydrolysis of this compound does not occur.

(2)

(Total 11 marks)

Q17.

(a) (i)

These four only

1

(ii)

Allow − NH₃⁺ and ⁺NH₃₋

1

(iii)2-amino-3-hydroxybutanoic acid

Ignore 1 in butan-1-oic acid

Do not penalise commas or missing hyphens

Penalise other numbers

1

(iv)

Allow –NH₃⁺ and ⁺NH₃₋

1

(b) (i)Condensation

Allow polyester

1

(ii)propane-1,3-diol

Must have e

Allow 1,3-propanediol

1

(c) (i)Addition

Not additional

1

(ii)

Allow monomers drawn either way round

Allow bond to F in CF₃

1

OR

1 for each structure within each pair

1

(d) c

If wrong, CE = 0

1

C-C or C-F bonds too strong

1

[11]

Q18.

A possible synthesis of the amino acid X is shown below.

(a) Name and outline a mechanism for Step 1.

(5)

(b) Give the IUPAC name of the product of Step 2.

(1)

(c) For Step 3, give the reagent, give a necessary condition and name the mechanism.

(3)

(d) At room temperature, the amino acid X exists as a solid.

(i) Draw the structure of the species present in the solid amino acid.

(1)

(ii)With reference to your answer to part (d)(i), explain why the melting point of the amino acid X is higher than the melting point of CH₃CH₂CH(OH)COOH.

(2)

(e) There are many structural isomers of X, CH₃CH₂CH(NH₂)COOH.

(i) Draw a structural isomer of X that is an ethyl ester.

(1)

(ii)Draw a structural isomer of X that is an amide and also a tertiary alcohol.

(1)

(iii) Draw a structural isomer of X that has an unbranched carbon chain and can be polymerised to form a polyamide.

(1)

(f) Draw the structure of the tertiary amine formed when X reacts with bromomethane.

(1)

(Total 16 marks)

Q18.

(a)

• allow :CN–

• M2 not allowed independent of M1, but

• allow M1 for correct attack on C+

• + rather than δ+ on C=O loses M2

• M3 is for correct structure including minus sign but lone pair is
part of M4

• Allow C_2H5

• M1 and M4 for lp and curly arrow

1

(b) 2-bromobutanenitrile

Allow 2-bromobutane-1-nitrile

1

(c) M1 ammonia or NH₃

Ignore temp or pressure

1

M2 excess (ammonia)excess tied to NH₃ and may score in M1 unless
contradicted

Ignore concentrated or sealed container, Acid loses conditions mark

1

M3 nucleophilic substitution

Allow close spelling

1

(d)(i)

Allow C₂H₅

Allow –CO₂^–

Allow ⁺NH₃–

Don’t penalize position of + on NH₃

1

(ii)M1 electrostatic forces between ions in XQOL

Allow ionic bonding.

1

Marks independent

M2 (stronger than) hydrogen bonding between CH₃CH₂CH(OH)COOH

CE mention of molecules of X or inter molecular forces between X loses both marks

1

(e)(i)

OR

Isomer of C₄H₉NO₂

Allow NH₂–

1

(ii)

Isomer of C4H₉NO₂allow NH₂–

Allow

1

(iii)H₂N–CH₂CH₂CH₂–COOHorH₂N–(CH₂)₃–COOH

Isomer of C₄H₉NO₂ allow NH₂–

OR

Do not allow –C₃H₆–

Beware – do not credit X itself

1

(f)

Answer has 6 carbons so NOT isomer of X

Allow C₂H₅

Must have bond from C to N not to methyl group

1

[16]

Q19.

The amino acids aspartic acid and phenylalanine react together to form a dipeptide.
This dipeptide can be converted into a methyl ester called aspartame.

Aspartame has a sweet taste and is used in soft drinks and in sugar-free foods for people with diabetes.

Hydrolysis of aspartame forms methanol initially. After a longer time the peptide link breaks to form the free amino acids. Neither of these amino acids tastes sweet.

(a) Apart from the release of methanol, suggest why aspartame is not used to sweeten foods that are to be cooked.

(1)

(b) Give the IUPAC name of aspartic acid.

(1)

(c) Draw the organic species formed by aspartic acid at high pH.

(1)

(d) Draw the zwitterion of phenylalanine.

(1)

(e) Phenylalanine exists as a pair of stereoisomers.

(i) State the meaning of the term stereoisomers.

(2)

(ii)Explain how a pair of stereoisomers can be distinguished.

(2)

(Total 8 marks)

Q19.

(a)Heating speeds up (hydrolysis / breaking of peptide bonds)

OR forms non-sweet (amino acids)

1

(b) (2-)aminobutanedioic acid OR

2 not necessary but penalise other numbers at start

(2-)aminobutane(-1,4-)dioic acid

1,4 not necessary but penalise other numbers and 1,4 must be in correct place (QoL)

1

(c)

allow –CO₂^–

allow NH₂–

1

(d)

allow –CO₂^–

allow +NH₃–

don’t penalize position of + on NH₃

1

(e)(i)M1 Compounds/molecules with same structural formula

Not just structure

1

M2But with bonds/atoms/groups arranged differently in space or in 3D

Allow –with different spatial arrangement of atom/bond/group

1

Independent marks

(ii)(Plane) polarised light

1

Rotated in opposite directions

Not bent or turned or twisted; not different directions (QoL)

1

[8]

Q20.

(a) Name compound Y, HOCH₂CH₂COOH

(1)

(b) Under suitable conditions, molecules of Y can react with each other to form a polymer.

(i) Draw a section of the polymer showing two repeating units.

(1)

(ii) Name the type of polymerisation involved.

(1)

(c) When Y is heated, an elimination reaction occurs in which one molecule of Y loses one molecule of water. The organic product formed by this reaction has an absorption at 1637cm^–1 in its infrared spectrum.

(i) Identify the bond that causes the absorption at 1637 cm^–1 in its infrared spectrum.

(1)

(ii) Write the displayed formula for the organic product of this elimination reaction.

(1)

(iii) The organic product from part (ii) can also be polymerised.
Draw the repeating unit of the polymer formed from this organic product.

(1)

(d) At room temperature, 2-aminobutanoic acid exists as a solid.
Draw the structure of the species present in the solid form.

(1)

(e) The amino acid, glutamic acid, is shown below.

Draw the structure of the organic species formed when glutamic acid reacts with each of the following.

(i) an excess of sodium hydroxide

(1)

(ii) an excess of methanol in the presence of concentrated sulfuric acid

(1)

(iii) ethanoyl chloride

(1)

(f) A tripeptide was heated with hydrochloric acid and a mixture of amino acids was formed. This mixture was separated by column chromatography.
Outline briefly why chromatography is able to separate a mixture of compounds.
Practical details are not required.

(3)

(Total 13 marks)

Q20.

(a) 3-hydroxypropanoic acid

allow 3-hydroxypropionic acid
must be correct spelling

1

(b) (i) must show trailing bonds

or can start at any point in the sequence, e.g.

not allow dimer

allow –O–CH₂CH₂COOCH₂CH₂CO–

or –CH₂CH₂COOCH₂CH₂COO–

ignore ( ) or n

NB answer has a total of 6 carbons and 4 oxygens

1

(ii) condensation (polymerisation)

Allow close spelling

1

(c) (i) C=C or carbon-carbon double bond

1

(ii)

must show ALL bonds including O–H

1

(iii) must show trailing bonds

allow polyalkene conseq on their c(ii)

ignore n

1

(d)

allow NH₃⁺—

allow COO^–

1

(e) (i)

In (e), do not penalise a slip in the number of carbons in the -CH₂CH₂– chain, but all must be bonded correctly

NB two carboxylate groups

Allow COONa or COO^– Na⁺ but not covalent bond to Na

allow NH₂–

1

(ii)

In (e), do not penalise a slip in the number of carbons in the
-CH₂CH₂– chain, but all must be bonded correctly

NB two ester groups

allow NH₂– or ⁺NH₃–

1

(iii)

In 4(e), do not penalise a slip in the number of carbons in the -CH₂CH₂– chain, but all must be bonded correctly

allow anhydride formation on either or both COOH groups (see below) with or without amide group formation

1

(f) M1 phase or eluent or solvent (or named solvent) is moving or mobile

1

M2 stationary phase or solid or alumina/silica/resin

1

M3 separation depends on balance between solubility or affinity
(of compounds) in each phase
OR
different adsorption or retention
OR
(amino acids have) different R_f values
OR
(amino acids) travel at different speeds or take different times

1

[13]

Q21.

(a)Consider the tripeptide shown below that is formed from three amino acids, K, L and M.

(i) Name the process by which the tripeptide is split into three amino acids.

(1)

(ii)Give the IUPAC name for the amino acid K.

(1)

(iii)Draw the structure of the zwitterion of amino acid L.

(1)

(iv) Draw the structure of the species formed by amino acid M at low pH.

(1)

(b)Consider the amino acid serine.

(i)Draw the structure of the product formed when serine reacts with an excess of CH₃Br

(1)

(ii)Draw the structure of the dipeptide formed by two molecules of serine.

(1)

(Total 6 marks)

Q21.

(a) (i) hydrolysis

not hydration

1

(ii) 2-aminopropanoic acid

ignore alanine
QoL

1

(iii)

allow –CO₂^–
allow ⁺NH₃–
don’t penalize position of + on NH₃

1

(iv)

allow –CO₂^–
allow ⁺NH₃–
don’t penalize position of + on NH₃

1

(b) (i)

allow –CO₂H

allow limit as

+ on N or outside [ ]

1

(ii)

allow –CO₂H allow –CONH– or –COHN–

allow NH₂–

allow limit as

1

[6]

Q22.

The three amino acids shown below were obtained by hydrolysis of a protein.

(a) (i) Draw the zwitterion of alanine.

(1)

(ii) Draw the species formed when valine is dissolved in an alkaline solution.

(1)

(iii) Draw the species formed by lysine at low pH.

(1)

(b) Draw the two dipeptides formed by the reaction of alanine with valine.

(2)

(c) Name a suitable method by which the mixture of amino acids formed by hydrolysis of the protein can be separated.

(1)

(Total 6 marks)

Q22.

(a) (i)

allow –CO₂^–
allow ⁺NH₃–
don’t penalize position of + on NH₃

1

(ii)

allow –CO₂^–
allow NH₂–
allow C₃H₇

1

(iii)

allow –CO₂H
allow ⁺NH₃–
don’t penalize position of + on NH₃

1

(b)

1

allow –CO₂H
allow NH₂–
allow C₃H₇
allow as zwitterions
if error in peptide link e.g.

if twice, penalise both times
not polymers
if wrong amino acid in both can score Max 1

1

(c) chromatography or electrophoresis

ignore qualification to chromatography

1

[6]

Q23.

(a) The structure below shows the repeating unit of a polymer.

By considering the functional group formed during polymerisation, name this type of polymer and the type of polymerisation involved in its formation.

(2)

(b) Draw the structure of the species present in solid aminoethanoic acid, H₂NCH₂COOH

(1)

(c) Explain why the melting point of aminoethanoic acid is much higher than that of hydroxyethanoic acid, HOCH₂COOH

(2)

(Total 5 marks)

Q23.

(a) polyamide or nylon (2,4)

(allow nylon without numbers but if numbers are present they must be correct)

1

condensation

1

(b)

1

(c) ionic bonding in aminoethanoic acid

(can only score if includes that aminoethanoic is ionic)

1

stronger attractions than Hydrogen bonding in hydroxyethanoic acid

(e.g. stronger Hydrogen bonding in aminoethanoic acid scores 0)

(mention of electrostatic forces between molecules scores 0)

1

[5]

Q24.

Consider the reaction sequence shown below.

(a) Name and outline a mechanism for the reaction in Step 1.

(5)

(b) (i) Name compound Q formed in Step 2.

(ii) Two stereoisomers are formed by the dehydration of Q. Give the structures of these two isomers and name the type of stereoisomerism shown.

(4)

(c) An isomer of Q which has the structure shown below is polymerised to form the biodegradeable polymer known as PHB.

(i) Draw the repeating unit of the polymer PHB.

(ii) Suggest a reason why the polymer is biodegradeable.

(2)

(d) The amino acid R is shown below.

(i) Draw the structure of the zwitterion formed by R.

(ii) Draw the structure of the major organic product formed when an excess of R is reacted with bromomethane.

(iii) Name the mechanism of the reaction which results in the formation of the product given in part (ii).

(3)

(Total 14 marks)

Q24.

(a) necleophilic addition;

1

M3 structure;

(be lenient on position of charge on CN– )
(M2 not allowed independent of M1,
but allow M1 for correct attack on C+
if M2 show as independent first.)
(+on C of C=O loses M2 but ignore δ+ if correct)
(M4 for arrow and lone pair (only allow for correct M3 or close))

4

(b) (i) 2-hydroxybutanoic acid

1

(ii)

1

geometric(al) or cis-trans

1

(c) (i)

(one unit only) (ignore brackets or n) (trailing bonds are needed)

1

(ii) can be hydrolysed

OR

can be reacted with/attacked by acid/base/nucleophiles/H₂O/OH^–;

1

(d) (i)

(allow –NH₃⁺)

1

(ii)

(or zwitterions product)

1

(iii) nucleophilic substitution;

1

[14]

Q25.

(a) The compound H₂C=CHCN is used in the formation of acrylic polymers.

(i) Draw the repeating unit of the polymer formed from this compound.

(ii) Name the type of polymerisation involved in the formation of this polymer.

(2)

(b) When the dipeptide shown below is heated under acidic conditions, a single amino acid is produced.

(i) Name this amino acid.

(ii) Draw the structure of the amino acid species present in the acidic solution.

(2)

(c) The repeating unit of a polyester is shown below.

(i) Deduce the empirical formula of the repeating unit of this polyester.

(ii) Draw the structure of the acid which could be used in the preparation of this polyester and give the name of this acid.

(iii) Give one reason why the polyester is biodegradable.

(4)

(Total 8 marks)

Q25.

(a) (i)

(Ignore n or brackets, but trailing bonds are essential)

1

(ii) Addition or radical

1

(b) (i) 2-aminobutanoic (acid)

1

(ii)

1

(c) (i) C₃H₄O₂

1

(ii)

1

(1,4-)butan(e)dioic (acid)

(allow succinic, but not dibutanoic nor butanedicarboxylic acid)

1

(iii) Can be hydrolysed / can react with acid or base or water /
can react with nucleophiles

1

[8]

Q26.

(a) Consider the following amino acid.

(i) Draw the structure of the amino acid species present in a solution at pH 12.

(ii) Draw the structure of the dipeptide formed from two molecules of this amino acid.

(iii) Protein chains are often arranged in the shape of a helix. Name the type of interaction that is responsible for holding the protein chain in this shape.

(3)

(b) Consider the hydrocarbon G, (CH₃)₂C=CHCH₃, which can be polymerised.

(i) Name the type of polymerisation involved and draw the repeating unit of the polymer.

(ii) Draw the structure of an isomer of G which shows geometrical isomerism.

(iii) Draw the structure of an isomer of G which does not react with bromine water.

(4)

(Total 7 marks)

Q26.

(a) (i)

(1)

ignore Na⁺ unless covalently bonded

(ii)

(1)

must be dipeptide, not polymer nor anhydride
allow –CONH– or –COHN–

allow zwitterion

(iii) hydrogen bonding (1)

QL

Allow with dipole-dipole or v derWaals, but not dipole-dipole etc alone

3

(b) (i) Type of polymerisation: addition(al) (1)

Repeating unit:

(1)

not multiples

allow n

(ii) CH₃CH=CHCH₂CH₃ (1) C₂H₅

(iii)

4

[7]

Q27.

The structures of the amino acids alanine and glycine are shown below.

(a) Give the systematic name for alanine.

(1)

(b) Alanine exists as a pair of stereoisomers.

(i) Explain the meaning of the term stereoisomers.

(ii) State how you could distinguish between the stereoisomers.

(4)

(c) Give the structural formula of the species formed by glycine at pH 14.

(1)

(d) When two amino acids react together, a dipeptide is formed. Give the structural formulae of the two dipeptides which are formed when alanine and glycine react together.

(2)

(e) Give the structural formula of the organic compound formed when glycine reacts with methanol in the presence of a small amount of concentrated sulphuric acid.

(1)

(Total 9 marks)

Q27.

(a) 2-amino(e) propanoic acid (1)

1

(b) (i) molecules with same structure / structural formula (1)
but with bonds (atoms or groups) arranged differently in
space (3D) (1)

(ii) Plane polarised light (1)
Rotated (equally) in opposite directions (1)

4

(c)

(1)

allow H₂NCH₂COO^–

Penalise NH₂‑ and OH‑ once per paper
but CH₃– is allowed

1

(d)

Not anhydrides; not repeating units

2

(e)

(1)

or H₂NCH₂COOCH₃

1

[9]

Q28.

Three sections of the proton n.m.r. spectrum of CH₃CHClCOOH are shown below.

(a) Name the compound CH₃CHClCOOH

(1)

(b) Explain the splitting patterns in the peaks at δ 1.72 and δ 4.44

(2)

(c) Predict the splitting pattern that would be seen in the proton n.m.r. spectrum of the isomeric compound ClCH₂CH₂COOH

(1)

(d) The amino acid alanine is formed by the reaction of CH₃CHClCOOH with an excess of ammonia. The mechanism is nucleophilic substitution. Outline this mechanism, showing clearly the structure of alanine.

(5)

(e) The amino acid lysine has the structure

Draw structures to show the product formed in each case when lysine reacts with

(i) an excess of aqueous HCl,

(ii) an excess of aqueous NaOH,

(iii) another molecule of lysine.

(3)

(Total 12 marks)

Q28.

(a) 2-chloropropanoic acid (1)

1

(b) δ 1.72 Doublet next to CH (1)

δ 4.44 Quartet next to CH₃ (1)

2

(c) Two triplets (1)

1

(d)

Allow S_N1

5

(e) (i)

(ii)

(iii)

Or anhydride

3

[12]