24. Enolate Chemistry: Reactions at the Alpha-Carbon

Predict the products of the following reactions.

(a) cyclopentyl methyl ketone + excess Cl₂ + excess NaOH

(b) 1-cyclopentylethanol + excess I₂ + excess NaOH

(c) propiophenone + excess Br₂ + excess NaOH

Which of the following compounds is most likely to undergo a haloform reaction?

Which compounds will give positive iodoform tests?

(a) 1-phenylethanol

(b) pentan-2-one

(c) pentan-2-ol

(d) pentan-3-one

(e) acetone

(f) isopropyl alcohol

Propose a mechanism for the reaction of cyclohexyl methyl ketone with excess bromine in the presence of sodium hydroxide.

Show how you would accomplish the following conversions in good yields. You may use any necessary reagents.

(c)

Provide the major product for the following reaction.

In the presence of excess base and excess halogen, a methyl ketone is converted to a carboxylate ion. The reaction is known as the haloform reaction because one of the products is haloform (chloroform, bromoform, or iodoform). Before spectroscopy became a routine analytical tool, the haloform reaction served as a test for methyl ketones: the formation of iodoform, a bright yellow compound, signaled that a methyl ketone was present. Why do only methyl ketones form a haloform?

Predict the products of the following reactions.

(b) 1-phenylethanol + excess I₂ in base