Question

What makes ethanoic acid a weaker electrophile than ethanoyl chloride?

Answer 1

Consider the leaving group on the ipso carbon: chloride versus hydroxide ion.

Explanation:

Acetyl chloride, `H_3C-C(=O)Cl`, has a `Cl^-` leaving group. Acetic acid, `H_3C-C(=O)OH`, has an `HO^-` leaving group. Of course, hydroxide is a much stronger base (and stronger nucleophile) than chloride, and the differential ease of substitution reflects this