Nucleophiles carboxylic acid derivatives

CARBOXYLIC ACID DERIVATIVES NUCLEOPHILIC ACYL SUBSTITUTION... 

Carboxylic Acid Derivatives Nucleophilic Acyl Substitution... 

Both stages involve more than one step and these steps differ in detail among the various carboxylic acid derivatives and for different reaction conditions This chapter is organized to place the various nucleophilic acyl substitutions into a common mechanis tic framework and to point out the ways m which individual classes differ from the rest... 

What structural features are responsible for the reactivity order of carboxylic acid derivatives Like the other carbonyl containing compounds that we ve studied they all have a planar arrangement of bonds to the carbonyl group Thus all are about the same in offering relatively unhindered access to the approach of a nucleophile They differ m the degree to which the atom attached to the carbonyl group can stabilize the carbonyl group by electron donation... 

The order of reactivity of carboxylic acid derivatives toward nucleophilic acyl sub stitution can be explained on the basis of the electron donating properties of sub stituent X The greater the electron donating powers of X the slower the rate... 

The first stage of the mechanism is exactly the same as for nucleophilic addition to the carbonyl group of an aldehyde or ketone Many of the same nucleophiles that add to aldehydes and ketones—water (Section 17 6) alcohols (Section 17 8) amines (Sections 17 10-17 11)—add to the carbonyl groups of carboxylic acid derivatives... 

Conversions of acid anhydrides to other carboxylic acid derivatives are illustrated m Table 20 2 Because a more highly stabilized carbonyl group must result m order for nucleophilic acyl substitution to be effective acid anhydrides are readily converted to carboxylic acids esters and amides but not to acyl chlorides... 

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