Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Benzene, $\text{C}_6\text{H}_6$, reacts with chloroethane, $\text{C}_2\text{H}_5\text{Cl}$, in the presence of a suitable catalyst to give ethylbenzene, $\text{C}_6\text{H}_5\text{C}_2\text{H}_5$. With the catalyst present, the ion $\text{C}_2\text{H}_5^+$ is produced. This ion then reacts with benzene.
(a)[1]

Complete the equation for the reaction of $\text{C}_2\text{H}_5\text{Cl}$ with this catalyst so that $\text{C}_2\text{H}_5^+$ is formed as one product. $\text{C}_2\text{H}_5\text{Cl} + \ldots \rightarrow \text{C}_2\text{H}_5^+ + \ldots$

(b)

Ethylbenzene reacts with more $\text{C}_2\text{H}_5\text{Cl}$, producing a mixture that contains 1,2-diethylbenzene and 1,4-diethylbenzene.

(b(i))[1]

Draw the structures of 1,2-diethylbenzene and 1,4-diethylbenzene.

(b(ii))[1]

Explain why there is very little 1,3-diethylbenzene in the product mixture.

(c)

1,2-diethylbenzene can be oxidised to benzene-1,2-dioic acid, $\text{C}_6\text{H}_4(\text{COOH})_2$.

(c(i))[1]

State the reagent and conditions used for this reaction.

(c(ii))[2]

Complete the overall equation for this reaction. An oxygen atom from the oxidising agent is shown as $[\text{O}]$. All of the atoms in the two ethyl groups are fully oxidised in this reaction. $(1,2\text{-diethylbenzene}) + \ldots [\text{O}] \rightarrow \text{C}_6\text{H}_4(\text{COOH})_2 + \ldots + \ldots$

(c(iii))[1]

Predict the number of peaks in the carbon-13 NMR spectrum of benzene-1,2-dioic acid.

(d)

The proton ($^1\text{H}$) NMR spectra of ethylbenzene, $\text{C}_6\text{H}_5\text{C}_2\text{H}_5$, in $\text{CDCl}_3$ and of benzene-1,2-dioic acid, $\text{C}_6\text{H}_4(\text{COOH})_2$, in $\text{CDCl}_3$ are shown. They have not been identified.

(d(i))[1]

Explain the use of $\text{CDCl}_3$, instead of $\text{CHCl}_3$, as the solvent when obtaining these spectra.

(d(ii))[3]

Identify the substance shown by the spectrum in Fig. 6.1, and complete Table 6.1.

(d(iii))[1]

Identify the substance shown by the spectrum in Fig. 6.2, and complete Table 6.2.

(d(iv))[1]

When D$_2$O is used as a solvent, the spectrum obtained is different from the spectrum in Fig. 6.2. Describe this difference and explain your answer.

(e)[1]

Benzene-1,2-dioic acid can be used to produce K. Suggest the name of this type of reaction.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: $\ce{C2H5Cl + AlCl3 -> C2H5+ + AlCl4^-}$

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