Question
Benzene, $\mathrm{C}_6 \mathrm{H}_6$, can be obtained from crude oil.
(a) Benzene reacts with bromine, in the presence of a suitable catalyst, forming bromobenzene as one product.
(i) Give the name or formula of the other product of this reaction. [1]
(ii) In the presence of the catalyst, bromine can be considered to form the electrophile $\mathrm{Br}^{+}$.
Complete the mechanism by which benzene reacts with $\mathrm{Br}^{+}$, using curly arrows to show the movement of electron pairs.
(iii) Name this mechanism. ……………………………………………………………………………………………………………………… [1]
(b) Benzene can be used as a starting material in the synthesis of cyclohexylmethanol, $\mathrm{C}_6 \mathrm{H}_{11} \mathrm{CH}_2 \mathrm{OH}$, as outlined below.
i) Identify a suitable reagent and a suitable catalyst for step 1.
reagent ……………………………………………………………………………………………………………….
catalyst ………………………………………………………………………………………………………………. [2]
(ii) Draw the structure of A
(iii) Identify suitable reagents for steps 3 and 4 .
step 3
$\operatorname{step} 4$[2]
(iv) Deduce the number of peaks in the carbon-13 NMR spectrum of cyclohexylmethanol.[1] [Total: 10]
▶️Answer/Explanation
Ans:
8(a)(i) HBr / hydrogen bromide [1]
a)(ii)
M1 curly arrow to $\mathrm{Br}^{+}$AND curly arrow from $\mathrm{C}-\mathrm{H}$ bond as shown [1] M2 correct intermediate [1]
(b)(i) reagent: chloroethane / bromoethane / iodoethane OR formula [1] catalyst: $\mathrm{FeCl}_3 / \mathrm{AlC}_3$ etc. [1]
(b)(ii)
(b)(iii) step $3=\mathrm{LiAlH}_4[1]$
step $4=\operatorname{Pt}$ AND $\mathrm{H}_2[1]$
8(b)(iv) 5 / five [1]