A-LevelChemistryIntroduction to organic chemistry9701/22 · Oct/Nov 2018 · Q420 Marks

The diagram shows a reaction sequence starting from ethanal. [Figure showing reaction sequence from ethanal to P, Q, R, S, W, Z, T and 2-aminopropane]

(a)(i)Draw the displayed formula of P.[1]
(a)(ii)Name the type of chemical reaction that occurs in reaction 3.[1]
(a)(iii)Write an equation to represent reaction 4. Use [O] to represent the oxidising agent. CH3CH(OH)CO2H +[1]
(a)(iv)State the reagents and conditions for reaction 4.[1]
(b)(i)Compound Q is formed as a mixture of two optical isomers. Explain what is meant by the term optical isomers.[1]
(b)(ii)Draw the two optical isomers of Q, showing clearly their three-dimensional structures.[2]
(c)R can be used to make a polymer, W, in two steps. [Figure showing R undergoing addition polymerisation to intermediate polymer, then NaOH(aq) to W] Draw one repeat unit of W.[3]
(d)(i)Compound Z, H2C=CHCH3, is produced from R. Z can be used in a two-step process to produce 2-aminopropane. In the first step, Z reacts with HBr to form two products. The structure of the product depends on which intermediate is formed, intermediate I or intermediate II. [Figure showing structures of intermediate I (secondary carbocation) and intermediate II (primary carbocation)] Explain why intermediate I is more likely to form than intermediate II.[2]
(d)(ii)When intermediate I forms, the product of the first step is T. Complete the diagram to show the mechanism for the conversion of Z to T. Include all relevant charges, partial charges, curly arrows and lone pairs. [Figure showing incomplete mechanism diagram for Z to T][3]
(d)(iii)T can then be converted to 2-aminopropane. [Figure showing T reacting with NH3/ethanol to form 2-aminopropane] Name the mechanism for this conversion.[1]
(e)(i)Compound S, CH3COCO2H, can be reduced by LiAlH4. Complete the equation using structural formulae to represent this reaction. Use [H] to represent the reducing agent. CH3COCO2H +[2]
(e)(ii)Other reducing agents containing Group 1 metal cations include LiBH4, NaBH4 and KBH4. The strength of the reducing agent depends on the size of its cation. Give the electronic configuration of the Na+ cation. 1s2[1]
(e)(iii)Suggest why ionic radius increases down Group 1.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] (displayed formula of 2-hydroxypropanenitrile)
[1] dehydration
[1] (H3C-CH(OH)-CO2H + [O] → H3C-CO-CO2H + H2O)
[1] Na2Cr2O7 / K2Cr2O7 AND (dilute) H2SO4 / H+(aq) / acidified
[1] (Molecules that are) non-super(im)posable mirror images
[1] M1 correct 3-d drawing of one isomer of Q
[1] M2 correct pair of 3-d structures of the optical isomers of Q
[3] H CO2Na | | -C -- C- | | H H OR -CH2CH(CO2Na)-
[1] M1 I experiences a (greater positive) inductive effect due to more alkyl groups OR I contains more electron donating alkyl groups (than II)
[1] M2 which stabilises the charge / reduces the charge (on the ion/intermediate) OR spreads the charge across the ion / molecule / intermediate
[1] M1 curly arrow from double bond to H of H–Br
[1] M2 curly arrow from H–Br bond to Br AND correct dipole on H—Br
[1] M3 curly arrow from lone pair on Br¯ to C⁺
[1] nucleophilic substitution
[1] M1 correct organic product CH3CHOHCH2OH
[1] M2 [H] present as reactant with H2O as product and balancing
[1] 1s2 2s2 2p6 (3s0)
[1] Ions/elements have more shells / energy levels (as the group is descended)