Question

он он te Acetyl adenosyl phosphate A sum Table 21.1. nclature rules for carboxylic acid derivatives is given in able 21.1 Nomenclature of Carboxylic Acid Derivatives Functional group Structure Name ending -ic acid (-carboxylic acid) Carboxylic acid -oyl halide (-carbonyl halide) 0 Acid halide anhydride Acid anhydride -amide (-carboxamide Amide -oate (-carboxylate) Ester RT 、NH2 (NHR, NR2) -thioate (-carbothioate) Thioester -oyl phosphate 0 Acyl phosphate 3.) List the functional groups shown in table 21.1 on page 817 in order of reactivity (omit the acyl phosphate). Explain why carboxylic acids are less reactive than acid chlorides.

Answer 1

The Nucleophilic acyl substitution reaction:-

The fact that the atom adjacent to the carbonyl carbon in carboxylic acid derivatives is an electronegative heteroatom – rather than a carbon like in ketones or a hydrogen like in aldehydes - is critical to understanding the reactivity of these functional groups. The carboxylic acid derivatives are attacked from one side of their trigonal planar carbonyl carbon by a nucleophile, converting this carbon to tetrahedral (sp3) geometry. In carboxylic acid derivatives, the acyl X group is a leaving group. the tetrahedral product formed from attack of the nucleophile on the carbonyl carbon is not the product: it is a reactive intermediate. The tetrahedral intermediate rapidly collapses: the carbon-oxygen double bond re-forms, and the acyl X group is expelled.
Cro Nu Nu
Carboxylic acids have conjugation which makes them stable i.e. unreactive or less reactive, whereas acid halides don't have such possibility and due to electronegative nature of halide groups the carbon becomes more electrophilic hence more reactive towards any nucleophilic attack. So the overall reactivity order is:-
0 SA' OR' oH Aoid chiond Mast Nh milu leasl iv
The acid chloride is most reactive and the amide is least reactive.