Carbonyl group substitution

Chapters 1 and 2 dealt with formation of new carbon-carbon bonds by reactions in which one carbon acts as the nucleophile and another as the electrophile. In this chapter we turn our attention to noncarbon nucleophiles. Nucleophilic substitution is used in a variety of interconversions of functional groups. We discuss substitution at both sp3 carbon and carbonyl groups. Substitution at saturated carbon usually involves the Sjv2 mechanism, whereas substitution at carbonyl groups usually occurs by addition-elimination. 

In the reaction of rnr-3,6-dimethyl-l,4-dioxane-2,5-dione (m.-lactide) with sulfur tetrafluoride in hydrogen fluoride solution, together with fluorination of both carbonyl groups, substitution of one of the tertiary hydrogen atom by fluorine also occurs a diastcrcomeric mixture of 2,3,3.6,6-pcntafluoro-2,5-dimethyl-l,4-dioxane (12) is formed in 75% yield (cf. Section 8.2.7.).166... 

Carboxylic acids, esters, and amides have their carbonyl groups bonded to an atom (O or N) that strongly attracts electrons. All three families undergo carbonyl-group substitution reactions, in which a group we can represent as -Y substitutes for the -OH, -OC, or -N group of the carbonyl reactant. 

One of the most important chemical transformations of carboxylic acids is their acid-catalyzed reaction with an alcohol to yield an ester. Acetic acid, for example, reacts with ethanol in the presence of H2SO4 to yield ethyl acetate, a widely used solvent. The reaction is a typical carbonyl-group substitution, with -OCH2CH3 from the alcohol replacing -OH from the acid. 

The most important reaction of esters is their conversion by a carbonyl-group substitution reaction into carboxylic acids. Both in the laboratory and in the body, esters undergo a reaction with water—a hydrolysis—that splits the ester molecule into a carboxylic acid and an alcohol. The net effect is a substitution of -OC by -OH. Although the reaction is slow in pure water, it is catalyzed by both acid and base. Base-catalyzed ester hydrolysis is often called saponification, from the Latin word sapo meaning "soap." Soap, in fact, is a mixture of sodium salts of long-chain carboxylic acids and is produced by hydrolysis with aqueous NaOH of the naturally occurring esters in animal fat. 

Click Coached Tutorial Problems for more practice using Table 19.1 to predict the position of the Equilibrium in Carbonyl Group Substitutions. 

Group Conditions (page 804) Coached Tutorial Problem Equilibrium in Carbonyl Group Substitutions (page 808)... 

Carbonylatlon of a halide ortriflate provides a direct route to a range of chain-extended acyl derivatives. A carbonyl group substituted with pdX X = halide or triflate) is a reactive acylating agent, rather like an... 

A carbonyl group substituted with an oxygen is less reactive than a carbonyl group substituted with a carbon due to resonance stabilization. The left carbonyl group has one such resonance interaction to stabilize it, whereas the right carbonyl group has two. 

The relative iron-olefin bond strength is evidenced by the ease of olefin substitution by phosphines. For complexes which contain olefins possessing a,j5 carbonyl substituents, the rate of olefin and carbonyl group substitution by PPh3 increases according... 

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