A-LevelChemistryHydrocarbons9701/22 · Feb/Mar 2018 · Q411 Marks

Cyclohexane is a colourless liquid used in industry to produce synthetic fibres. A reaction scheme involving cyclohexane is shown. [Figure 4.1: Reaction scheme showing cyclohexane via reaction 1 to chlorocyclohexane, and chlorocyclohexane via reaction 2 to cyclohexene]

(a)(i)State the essential condition required for reaction 1 to occur.[1]
(a)(ii)Complete the table to give details of the mechanism in reaction 1. name of step | reaction initiation | Cl2 → 2Cl• propagation | [cyclohexane structure] + •Cl → [cyclohexyl radical structure] + .......... propagation | [cyclohexyl radical structure] + Cl2 → [chlorocyclohexane structure] + .......... termination | [cyclohexyl radical structure] + •Cl → ..........[4]
(b)Name the type of reaction that occurs in reaction 2.[1]
(c)(i)Identify the reagents and conditions for the conversion of cyclohexene into adipic acid.[2]
(c)(ii)Suggest three main differences between the infra-red spectra of cyclohexene and adipic acid. In each case, identify the bond responsible and its characteristic absorption range (in wavenumbers).[3]

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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] ultraviolet / UV light
[4] initiation: Cl2 → 2Cl•
propagation: •Cl + [cyclohexane structure] → [cyclohexyl radical structure] + HCl
propagation: [cyclohexyl radical structure] + Cl2 → [chlorocyclohexane structure] + •Cl
termination: •Cl + •Cl → Cl2
termination: [cyclohexyl radical structure] + •Cl → [chlorocyclohexane structure]
termination: [cyclohexyl radical structure] + [cyclohexyl radical structure] → [bicyclohexyl structure]
[1] elimination
[2] acidified AND KMnO4
hot AND concentrated)
[max 3] cyclohexene would have absorption at 1500–1680 (cm⁻¹) because of C=C (and adipic acid would not)
cyclohexene would have absorption at 3000–3100 (cm⁻¹) because of =C-H/C—H in alkene (and adipic acid would not)
adipic acid would have absorption at 2500–3000 (cm⁻¹) because of O—H/CO2—H (and cyclohexene would not)
adipic acid would have absorption at 1040–1300 (cm⁻¹) because of C—O (and cyclohexene would not)
adipic acid would have absorption at 1640–1750 (cm⁻¹) because of C=O (and cyclohexene would not)

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