Page 647 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

7

Addition, Condensation

and Substitution Reactions

of Carbonyl Compounds

Introduction

The carbonyl group is one of the most prevalent of the functional groups and is involved
in many synthetically important reactions. Reactions involving carbonyl groups are
also particularly important in biological processes. Most of the reactions of aldehydes,
ketones, esters, carboxamides, and the other carboxylic acid derivatives directly involve
the carbonyl group. We discussed properties of enols and enolates derived from
carbonyl compounds in Chapter 6. In the present chapter, the primary topic is the
mechanisms of addition, condensation and substitution reactions at carbonyl centers.
We deal with the use of carbonyl compounds to form carbon-carbon bonds in synthesis
in Chapters 1 and 2 of Part B.
In many reactions at carbonyl groups, a key step is the addition of a nucleophile,
which generates a tetracoordinate carbon atom. The overall course of the reaction is
then determined by the fate of this tetrahedral intermediate. Addition occurs when
the tetrahedral intermediate goes directly on to product. Condensation occurs if the
carbonyl oxygen is eliminated and a double bond is formed. Substitution results
when one of the groups is eliminated from the tetrahedral intermediate to re-form a
carbonyl group.

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