15.18 : 羟醛脱水生成烯酮：酸催化羟醛缩合

The β-hydroxy ketone dehydrates in acidic conditions via an E1 elimination reaction to form an enone.

The E1 elimination proceeds through two distinct steps: ionization and deprotonation.

In the first step, the hydroxyl group in the presence of an acid functions as a Bronsted–Lowry base and accepts a proton to yield a hydrated hydroxyl group. Then, a neutral water molecule departs to give a tertiary carbocation intermediate.

Finally, the chloride ion abstracts the hydrogen atom from the α carbon to form an enone as the product.