Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Long-chain alkanes such as 4-methylheptane may be ‘cracked’ to make hydrocarbons with shorter chains.
(a(i))[1]

State the conditions needed for this reaction to happen.

(a(ii))[1]

Suggest the structure of $B$, given that $B$ has molecular formula $\text{C}_3\text{H}_8$.

(a(iii))[3]

Compounds $C$, $D$ and $E$ are isomers with molecular formula $\text{C}_5\text{H}_{10}$. When heated with concentrated acidified $\text{KMnO}_4$, compound $C$ forms $\text{CO}_2$ and compound $F$ ($\text{C}_4\text{H}_8\text{O}_2$). Compounds $D$ and $E$ each produce a $1{:}1$ mixture of compounds $G$ ($\text{C}_2\text{H}_4\text{O}_2$) and $H$ ($\text{C}_3\text{H}_6\text{O}_2$). Suggest structures for compounds $C$-$H$.

(a(iv))[1]

Name the kind of isomerism shown by $D$ and $E$.

(b(i))[1]

How is this reaction generally carried out?

(b(ii))[1]

State the type of reaction taking place here.

(b(iii))[2]

Draw the mechanism for this reaction, including the structures of any intermediates, plus any dipoles, lone pairs and curly arrows needed to show electron movement.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Heat, using a catalyst such as $\mathrm{Al_2O_3/SiO_2}$

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