A-LevelChemistryNitrogen and sulfur9701/42 · May/June 2025 · Q711 Marks

2-aminobutane, CH3CH(NH2)CH2CH3, exists as a mixture of two enantiomers. Define enantiomers.

(a)2-aminobutane, CH3CH(NH2)CH2CH3, exists as a mixture of two enantiomers. Define enantiomers.[1]
(b)(i)Explain why an aqueous solution of 2-aminobutane has a pH greater than 7. Include an equation in your answer.[2]
(b)(ii)A 0.10 moldm⁻³ solution of diethylamine, (CH3CH2)2NH, has a higher pH than a 0.10 moldm⁻³ solution of 2-aminobutane, CH3CH(NH2)CH2CH3. Suggest why.[2]
(b)(iii)(CH3CH2)2NH reacts with ethanoic acid, CH3COOH. Complete the equation for this reaction. (CH3CH2)2NH + CH3COOH → ............................................[1]
(b)(iv)(CH3CH2)2NH reacts with ethanoyl chloride, CH3COCl. Complete the equation for this reaction. (CH3CH2)2NH + CH3COCl → ............................................[1]
(c)(i)Table 7.1 shows monomers that can undergo polymerisation. [Table 7.1] Complete Table 7.1.[1]
(c)(ii)Ethanedioic acid, HOOCCOOH, can react with propane-1,3-diamine, H2NCH2CH2CH2NH2, to form polymer W. Draw a section of polymer W showing only one repeat unit. The new functional group formed should be displayed.[2]
(c)(iii)Poly(alkenes) biodegrade very slowly. Explain why.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[1] rotate the plane of polarised light equally in the opposite direction
[1] M1: nitrogen/N can accept / bond to a proton / H+ ion OR donation of lone pair/electrons on the nitrogen / N to a proton / H+ ion
[1] M2: CH3CH(NH2)CH2CH3 + H2O → CH3CH(NH3+)CH2CH3 + OH-
[1] M1: more electron donating alkyl / ethyl group on N/NH (in diethylamine) OR two electron donating alkyl / R / alkane / ethyl group on N/NH (in diethylamine)
[1] M2: increase electron density on N OR make lone pair on N more available (to accept H+)
[1] (CH3CH2)2NH + CH3COOH → (CH3CH2)2NH2+ CH3COO-
[1] (CH3CH2)2NH + CH3COCl → CH3CON(CH2CH3)2 + HCl
[1] CH2CHCH3COOH addition
[1] (benzene ring with OH and Cl as substituents, not explicitly drawn in MS) condensation
[1] CH3CH(NH2)COOH condensation
[1] M1: correct displayed amide linkage with an adjacent C=O (to CO) and C(H2) to NH
[1] M2: rest of the dipeptide correct (only one repeat unit) with continuation bonds
[1] they are chemically inert / difficult to hydrolyse / C-C bonds are non-polar

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