Question

One of the steps in metabolism of fats is the reaction of an unsaturated acyl coA with water to give a $\beta$- hydroxyacyl CoA. Propose a mechanism.

Short answer

The first step of the mechanism is-

Step-by-step solution

Introduction

The reactant given in the reaction is an$\alpha ,\beta$ unsaturated type of aldehyde/ketonic compound. To this water can be added reversibly to an unsaturated acyl CoA to give a $\beta$- hydroxyacyl CoA. This is one of the steps in the metabolism of fats and also an example of Conjugate nucleophilic addition to an unsaturated aldehyde or ketone.

Mechanism

In the first step of the reaction, the OH adds to the C=C or $\alpha$carbon (carbon atom next to carbonyl carbon is $\alpha$carbon while next to the $\alpha$ carbon is the $\beta$ carbon). Initially, an enolate ion is obtained which then undergoes a protonation to yield finally _$\beta$

-hydroxyacyl-CoA. This is also known as 1,4 addition. The mechanism can be represented as-