Chapter 20, Problem 20.4YT

Interpretation Introduction

Interpretation:

The mechanism for the given reaction is to be completed by adding curved arrows to show the movement of electrons.

Concept introduction:

Transesterification reaction is the one in which one ester is converted to another. A typical reaction involves a nucleophile and a carboxylic acid derivative. It is called a nucleophilic addition–elimination mechanism, which describes the two steps that take place.

Step 1 is a nucleophilic addition in which a nucleophile attacks the electron poor carbonyl carbon. This forces the pair of electrons from the initial C=O to oxygen atom, which generates a negative charge in it. The product of that step is a tetrahedral intermediate, which, in Step 2, undergoes nucleophile elimination. A lone pair of electrons on the negatively charged O atom is used to regenerate the C=O double bond, and the leaving group departs as methoxide ion.