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 Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O 
Ch 17 contents

Nucleophilic Addition

Nucleophilic addition of aldehydes and ketones
Nucleophilic addition reactions are an important class of reactions that allow the interconversion of C=O into a
range of important functional groups.

What does the term "nucleophilic addition" imply ?

A nucleophile, Nu-, is an electron rich species that will react with an electron poor species (here the C=O)
An addition implies that two systems combine to a single entity.
There are three fundamental events in a nucleophilic addition reaction:
  1. formation of the new s bond between the nucleophile, Nu, to the electrophilic C of the C=O group
  2. breaking of the p bond to the O resulting in the formation of an intermediate alkoxide
  3. protonation of the intermediate alkoxide to give an alcohol derivative
Depending on the reactivity of the nucleophile, there are two possible general scenarios:
Addition of strong nucleophiles to aldehydes and ketones

            Examples of such nucleophilic systems are :  RMgX, RLi, RC≡CM, LiAlH4, NaBH4

Addition of weaker nucelophiles under acidic conditions to aldehydes and ketones
            Examples of such nucleophilic systems are :  H2O, ROH, R-NH2
The protonation of a carbonyl gives a structure that can be redrawn in another resonance form that reveals the electrophilic character of the C since it is a carbocation. resonance in a protonated ketone

The reactions on the following pages are catalogued based on the nature of the nucleophilic atom involved.
In most cases it is useful to indentify the mechanism in each case in terms of the two general schemes presented above.

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© Dr. Ian Hunt, Department of Chemistry, University of Calgary