9701 MCQ Solution 28

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Question 28: [Organic > Carbonyl Compounds]:

Ethanal may be converted into a three-carbon acid in a two-step process.

Which compound is the intermediate?

A CH₃CO₂H

B CH₃CN

C CH₃CH₂CN

D CH₃CH(OH)CN

Reference: Past Exam Paper – November 2002 Paper 1 Q28

Solution 28:

Answer: D.

As the number of carbons is increasing from 2 (ethanal) to 3, the addition of a cyanide ion is necessary as that is the only method to increase the carbon chain length. Therefore A is eliminated.

B is also eliminated as there are now only two carbons and it is impossible to get that compound from ethanal.

C has 3 carbons however does not have an alcohol group which can be oxidized to form an acid.

D is the only option that satisfies all conditions.