Chemistry 9701 · AS & A Level · Organic synthesis

Organic synthesis — practice question

Compound $Q$ may be synthesised from chlorobenzene in seven steps by the route shown in Fig. 5.1.
(a(i))[1]

Write the equation for how the electrophile is formed in step $1$.

(a(ii))[3]

Complete the mechanism in Fig. 5.2 for step $1$, the alkylation of chlorobenzene. Add all the relevant curly arrows and charges, and draw the intermediate structure.

(a(iii))[1]

Step $2$ is an oxidation reaction. Construct an equation for the reaction in step $2$. Use $[O]$ to represent an atom of oxygen from an oxidising agent.

(a(iv))[2]

Suggest reagents for changing $K$ into $M$ in steps $3$ and $4$. Step $3$. Step $4$.

(a(v))[1]

Identify the type of reaction that occurs in step $5$.

(a(vi))[1]

Step 7 takes place when P is heated with a weak base such as $\text{K}_2\text{CO}_3$(aq). Suggest why a strong base such as NaOH(aq) is not used for this reaction.

(a(vii))[1]

Q is optically active. Explain the meaning of optically active.

(a(viii))[2]

Give two reasons why it might be desirable to synthesise a single optical isomer of Q for use as a drug.

(b(i))[3]

The $pK_a$ of aspirin is $3.49$. $75\,\text{mg}$ of aspirin dissolves in water to form $100\,\text{cm}^3$ of an aqueous solution. Calculate the pH of this solution. $[M_r\,\text{aspirin},\,180.0]$

(b(ii))[2]

Aspirin undergoes acid hydrolysis in the stomach. Give the structures of the organic products of this acid hydrolysis.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: Equation: AlCl$_3$ + CH$_3$Cl $\rightarrow$ AlCl$_4^-$ + CH$_3^+$.

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