Question

Terminal alkynes react with and water to yield bromo ketones. For example:

Propose a mechanism for the reaction. To what reaction of alkenes is

the process analogous?

Short answer

Mechanism of given reaction

1. Attack of nucleophile alkyne on the Bromine atom and formation of three membered ring

2. Ring opening by a hydronium ion

3. Tautomerization takes place in which alcohol is converted into ketone

Step-by-step solution

Formation of ketones

An alkyne acts as a nucleophile and attacks on the${\mathbf{Br}}_{\mathbf{2}}$, resulting in the formation of a cyclic ring. The three-membered ring is highly strained and thus unstable. This is what causes the ring to open and then ketone to form.

Mechanism of given reaction

1. Attack of nucleophile alkyne on the Bromine atom and formation of three membered ring

2. Ring opening by a hydronium ion

3. Tautomerization takes place in which alcohol is converted into ketone

Analogous mechanism

Formation of a halohydrin is an analogous mechanism to given mechanism.