A Preview of Oxidation and Reduction

Problem 20.2 Which compounds undergo nucleophilic addition and which undergo substitution  

Which compound in each pair is more reactive towards nucleophilic attack  

To show how these general principles of nucleophilic substitution and addition apply to carbonyl compounds, we are going to discuss oxidation and reduction reactions, and reactions with organometallic reagents—compounds that contain carbon-metal bonds. We begin with reduction to build on what you learned previously in Chapter 12. 

Recall the definitions of oxidation and reduction presented in Section 12.1  

Oxidation results in an increase in the number of C-or a decrease in the number of C-H bonds. Reduction results in a decrease in the number of C-or an increase in the number of C - H bonds. 

Carbonyl compounds are either reactants or products in many of these reactions, as illustrated in the accompanying diagram. For example, because aldehydes fall in the middle of this scheme, they can be both oxidized and reduced. Carboxylic acids and their derivatives (RCOZ), on the other hand, are already highly oxidized, so their only useful reaction is reduction. 

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