Which of the following reactions is an example of a nucleophilic substitution reaction in organic chemistry?

• A. Esterification of carboxylic acids
• B. Hydrogenation of alkenes
• C. Dehydration of alcohols
• D. $S_{\mathrm{N}}2$ reaction of alkyl halides

Answer: (D)

Verified step by step guidance

1. Understand the concept of nucleophilic substitution reactions: These reactions involve the replacement of a leaving group in a molecule by a nucleophile. The two main types are SN1 and SN2 reactions.
2. Identify the characteristics of an SN2 reaction: It is a bimolecular nucleophilic substitution where the nucleophile attacks the substrate from the opposite side of the leaving group, leading to an inversion of configuration.
3. Analyze the given options: Esterification of carboxylic acids involves the formation of an ester from a carboxylic acid and an alcohol, which is not a nucleophilic substitution. Hydrogenation of alkenes involves the addition of hydrogen, not substitution. Dehydration of alcohols involves the removal of water, not substitution.
4. Focus on the SN2 reaction of alkyl halides: In this reaction, an alkyl halide undergoes substitution where the halide ion (leaving group) is replaced by a nucleophile, fitting the definition of a nucleophilic substitution.
5. Conclude that the SN2 reaction of alkyl halides is the correct example of a nucleophilic substitution reaction among the given options.