A-LevelChemistryIntroduction to organic chemistry9701/21 · May/June 2024 · Q614 Marks

V shows stereoisomerism. [Figure 6.1]

(a)V shows stereoisomerism. [Figure 6.1]
(a)(i)Explain what is meant by stereoisomerism.[1]
(a)(ii)Deduce the number of stereoisomers of V. Explain your reasoning.[2]
(a)(iii)Deduce the molecular formula of V.[1]
(a)(iv)Name all the functional groups present in V.[1]
(b)[Figure 6.2] shows two reactions involving V.
(b)(i)Identify the role of reagent T for each functional group that reacts in reaction 1.[1]
(b)(ii)Suggest the identity of reagent U in reaction 2.[1]
(c)Both functional groups in one molecule of Y react with an inorganic reagent to form one molecule of Q and one molecule of methanol, CH3OH, as shown in [Figure 6.3].
(c)(i)Part of the mass spectrum for Q is shown in [Figure 6.4]. Only peaks with m/e greater than 198 are shown. Calculate the relative abundance, x, of the peak at m/e = 201. Show your working. x =[2]
(c)(ii)Q contains only hydroxyl functional groups. Complete Table 6.1 to show the observations that occur when 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) is added to separate samples of Y and Q. Table 6.1 observation on addition of 2,4-DNPH reagent Y Q[1]
(c)(iii)Under certain conditions, 0.0020 mol of Q reacts with an excess of sodium to produce a total of 44.8 cm³ of gas at s.t.p. Calculate the number of hydroxyl groups present in a molecule of Q. Show your working. number of hydroxyl groups =[2]
(c)(iv)Use Table 6.2 to describe and explain two differences between the infrared spectrum of Y and Q in the region above 1500cm-1. Table 6.2 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers)/cm-1 C-O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide 1640–1690 carbonyl, carboxyl 1670–1740 ester 1710–1750 C=N nitrile 2200–2250 C-H alkane 2850–2950 N-H amine, amide 3300–3500 O-H carboxyl 2500–3000 hydroxy 3200–3650[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] (molecules with the) same structural formula (and same molecular formula) with different arrangement of atoms / groups in space
[2] M1 number of stereoisomers = 8
M2 reasoning: 2 chiral centres AND 1 C=C (producing a cis-and trans or geometrical pair)
[1] C13H20O3
[1] ester AND carbonyl / ketone AND C=C (bond) / alkene
[1] reducing agent for C=O AND C=C
[1] sodium borohydride / NaBH4
[2] M1 deduce n = 12 (from Y – 1C (in methanol))
M2 (100 × x) ÷ (1.1 × 100) = 12 (so) x = 13.2
[1] Both correct for one mark
Y: orange precipitate
Q: no precipitate
[2] ROH + Na → RONa + 1/2H2
(0.002 mol Q produced 0.002 mol H2 gas so) 2 OH groups
M1 answer indicates that OH group(s) in Q react with Na to produce the H2 in the ratio 1 mol OH : 1½ mol H2
M2 uses data to show 2OH groups
[2] M1 Y will have absorption / peak / trough between 1670–1740 due to C=O (Q will not)
M2 Q will have absorption / peak / trough between 3200–3650 due to O-H (Y will not)