Carbonyls, carboxylic acids and chirality

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   Ethanoyl chloride, $\text{CH}_3\text{COCl}$, reacts readily at room temperature.

   (a) Write an equation for its reaction with water.

   (b) Write an equation for its reaction with ethanol.

   (c) Give one advantage of using ethanoyl chloride rather than ethanoic acid to make ethyl ethanoate.

   Mark scheme

   • (a) $\text{CH}_3\text{COCl} + \text{H}_2\text{O} \rightarrow \text{CH}_3\text{COOH} + \text{HCl}$ (1)
   • (b) $\text{CH}_3\text{COCl} + \text{C}_2\text{H}_5\text{OH} \rightarrow \text{CH}_3\text{COOC}_2\text{H}_5 + \text{HCl}$ (1)
   • (c) The reaction is not reversible so gives a higher yield / is fast at room temperature without a catalyst (1)
2. Question 24 marks

   Propanal reacts with hydrogen cyanide (in the presence of cyanide ions) to form 2-hydroxybutanenitrile, $\text{CH}_3\text{CH}_2\text{CH(OH)CN}$.

   Explain why the product has a chiral centre but the product mixture does not rotate the plane of plane-polarised light.

   Mark scheme

   • The carbon bonded to OH has four different groups attached ($\text{H}$, , , ), so it is a chiral centre (1)