Chapter 7
Elimination Reactions
 
I.Introduction
In this module, different types of elimination reactions are described. From a practical standpoint, elimination reactions widely used for the generation of double and triple bonds in compounds from a saturated precursor molecule. The presence of a good leaving group is a prerequisite in most elimination reactions. Traditional classification of elimination reactions, in terms of the molecularity of the reaction is employed. How the changes in the nature of the substrate as well as reaction conditions affect the mechanism of elimination are subsequently discussed. The stereochemical requirements for elimination in a given substrate and its consequence in the product stereochemistry is emphasized.

Objective and Outline

  • beta-eliminations
  • E1, E2 and E1cB mechanisms
  • Stereochemical  considerations of these reactions
  • Examples of E1, E2 and E1cB reactions
  • Alpha eliminations and generation of carbene
I.Basics

Elimination reactions involve the loss of fragments or groups from a molecule to generate multiple bonds.

A generalized equation is shown below for 1,2-elimination wherein the X and Y from two adjacent carbon atoms are removed,

Three major types of elimination reactions are:

α-elimination : Two atoms or groups are lost from the same atom. It is also known as 1,1-elimination.
  Both H and X are removed from carbon atom here