A-LevelChemistryAnalytical techniques9701/42 · Feb/Mar 2018 · Q89 Marks

Cumin is a spice used to flavour food. Two compounds responsible for its flavour are cuminaldehyde and cuminyl alcohol. [Figure showing structures of cuminaldehyde and cuminyl alcohol]

(a)(i)Deduce the number of peaks that would be present in the ¹³C NMR spectrum of cuminyl alcohol. number of peaks[1]
(a)(ii)Identify two bonds that are responsible for the differences in the infra-red spectra of cuminaldehyde and cuminyl alcohol, and state their absorption ranges. [Table with columns 'bond responsible for the difference', 'absorption range in the infra-red spectrum/cm⁻¹ (cuminaldehyde)', 'absorption range in the infra-red spectrum/cm⁻¹ (cuminyl alcohol)'][2]
(b)(i)Cuminyl alcohol can be synthesised from benzene by the following route. [Reaction scheme showing 4 steps from benzene to cuminyl alcohol] Suggest reagents and conditions for steps 1–4. step 1 step 2 step 3 step 4[4]
(b)(ii)Name the mechanism of step 2 and state the type of reaction in step 4. mechanism of step 2 type of reaction in step 4[2]

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Mark scheme

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

[1] 7 peaks
[2] bond responsible for the difference | absorption range in the infra-red spectrum/cm⁻¹ ---------------------------------|--------------------------------------------- cuminaldehyde | cuminyl alcohol C=O | 1670–1740 OH | 3200–3600 Or C-O | 1000–1260
[4] step 1 heat with AlCl3 + (CH3)2CHCl or CH3CH=CH2 step 2 heat with AlCl3 + CH3COCl step 3 NaOH + I2 (or Cl2) (then H+) step 4 LiAlH4 (in dry ether)
[2] step 2 electrophilic (aromatic) substitution step 4 reduction

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