9701 MCQ Solution 22

Question 22: [Organic > Hydrocarbons]:

Chloroethane is used as a starting material for the production of ‘time-release capsules’ in pharmaceutical products. One way of preparing chloroethane is to react chlorine and ethane in the presence of ultraviolet light.

Which statement is correct about the first stage of the mechanism of this reaction?

A The Cl – Cl bond is split homolytically.

B The Cl – Cl bond is split heterolytically.

C The C – H bond is split homolytically.

D The C – H bond is split heterolytically.

Reference: Past Exam Paper – November 2002 Paper 1 Q22

Solution 22:

Answer: A.

This reaction is a free radical substitution, where an alkane reacts with a halogen to form a halogenoalkane. The first step is known as chain initiation in which the halogen’s diatomic molecule splits homolytically to form 2 halogen free radicals. In this case the Cl₂ molecule splits.