Question

The rate of solvolysis of `CH_3COCl` is greater than `CH_3CH_2Cl`. why?

Answer 1

Here's my understanding of the reaction.

Explanation:

Solvolysis is the reaction of a substrate with the solvent.

For example, if the solvent is methanol, the solvolysis of acetyl chloride would be represented as:

The mechanism involves an in-plane `S_text(N)2` displacement of the chloride ion.

It appears to be an `S_text(N)1^'` reaction because the concentration of the solvent is effectively a constant.

If we compare this reaction with the solvolysis of ethyl chloride (below), we see two differences.

(1) The carbonyl carbon in acetyl chloride is `"sp"^2` hybridized, while the α carbon in ethyl chloride is `"sp"^3` hybridized.

The carbonyl carbon has more `"s"` character, so it is more electronegative. It pulls the electrons in the `"C-Cl"` bond closer to itself.

This weakens the `"C-Cl"` bond and makes it easier to remove. Hence, the reaction is faster.

(2) The carbonyl carbon has a resonance contributor that puts more positive charge on the carbon atom.

This makes the carbonyl more susceptible to attack by a nucleophile. It lowers the activation energy, so the reaction is faster.