The proton NMR spectrum of compound E in the solvent CDCl3 is shown. The molecular formula of compound E is C9H10O2. [Figure of proton NMR spectrum, with relative integral values of 3, 2, 2, and 5 for peaks from right to left (low to high δ) respectively. Small peak at δ=0 is TMS.]
- (a)Explain why CDCl3 is used as a solvent instead of CHCl3.[1]
- (b)Explain why TMS is added to give the small peak at chemical shift δ = 0.[1]
- (c)Compound E is hydrolysed by hot NaOH(aq), giving two organic products only. One of these products is ethanol. Name the functional group in compound E that is hydrolysed by hot NaOH(aq).[1]
- (d)(i)Describe and explain the splitting patterns of the peaks at δ = 1.4 and δ = 4.3.[2]
- (d)(ii)Each molecule of compound E contains five protons which give rise to the peaks between δ = 7.0 and δ = 8.5. Identify the functional group in compound E which contains these protons.[1]
- (d)(iii)Give the structural formula of compound E.[1]
- (e)The mass spectrum of compound E includes fragment ions with m/e values of 29 and 77. Give the formulae of these fragment ions.[2]
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 2020). The mark or mark type is shown in brackets.
- [1] (because CDCl3 / it) does not give a peak OR because CHCl3 does give a peak
- [1] as a standard / reference for (chemical shift measurements)
- [1] ester
- [1] (d)(i) (δ = 1.4) triplet
- [1] (d)(i) (δ = 1.4) two H on neighbouring C atom
- [1] (d)(i) (δ = 4.3) quartet / quadruplet
- [1] (d)(i) (δ = 4.3) three H on neighbouring C atom
- [2] (d)(i) mark as ✓✓
- [1] aryl group / arene / phenyl
- [1] (d)(iii) Structure for ethyl benzoate (benzene ring with COOCH2CH3) OR C6H5CO2C2H5
- [1] CH3CH2⁺ / C2H5⁺
- [1] C6H5⁺
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