Chemistry 9701 · AS & A Level · Carbonyl compounds

Carbonyl compounds — practice question

Lactones are cyclic esters. When the conditions are suitable, they are produced from molecules that contain both an alcohol functional group and a carboxylic acid functional group. Equation 1 gives one example of lactone formation. Fig. 5.1 illustrates the synthesis of lactone P from compound M.
(a(i))[1]

M reacts with hot concentrated acidified $\text{KMnO}_4(\text{aq})$ to produce N, $\text{C}_6\text{H}_{10}\text{O}_3$, in reaction 1. Draw the structure of N.

(a(ii))[1]

N is reduced by $\text{NaBH}_4$ to form 5-hydroxyhexanoic acid in reaction 2. Write an equation for reaction 2 using molecular formulae. In the equation, use $[\text{H}]$ to show one hydrogen atom from the reducing agent.

(a(iii))[2]

Reaction 2 is a nucleophilic addition. Suggest why reaction 2 produces a mixture of two organic compounds.

(a(iv))[1]

Draw lactone P, the product obtained in reaction 3.

(b)[2]

A student follows the progress of reaction 2 by using infrared spectroscopy. Use Table 5.1 to suggest why it is hard to distinguish between N and 5-hydroxyhexanoic acid using infrared spectroscopy.

(iv)[1]

Draw lactone P, the product obtained in reaction 3.

(c)[2]

Unknown lactone Q is examined by mass spectrometry. Table 5.2 gives information from the mass spectrum. Use these data to deduce the structure of Q. Show your working.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: The correct structure of compound $N$ is shown.

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