Aryl halides such as chlorobenzene are far less reactive towards nucleophilic substitution than alkyl halides because
Correct answer: C. a lone pair on the halogen is delocalised into the ring, giving the carbon to halogen bond partial double bond character
- A. the benzene ring repels all nucleophiles equally
- B. chlorine is not electronegative in aromatic compounds
- C. a lone pair on the halogen is delocalised into the ring, giving the carbon to halogen bond partial double bond character
- D. aryl halides are ionic
Explanation
Overlap between the halogen lone pair and the ring pi system shortens and strengthens the bond, so the halogen is a much poorer leaving group and substitution requires extreme conditions of temperature and pressure. The carbon involved is also sp2 hybridised and holds its electrons more tightly. This is why chlorobenzene does not give a precipitate with silver nitrate on warming while chloroethane does.
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About Nomenclature, Structure and Reactivity
Alkyl halides are named by selecting the longest carbon chain and locating the halogen substituent, while their structures are classified as primary, secondary or tertiary. Their reactivity includes nucleophilic substitution and elimination, with the behaviour of leaving groups and the distinction between SN1 and SN2 mechanisms linked to substrate structure.
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458 free Alkyl Halides MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
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