Functional Classes II, Reactions - Organic Chemistry Concepts: An EFL Approach - page 141

The first step of nucleophilic addition goes as we expect. It gives the tetrahedral
intermediate. However, instead of adding a proton to complete the addition, the good
halide leaving group is eliminated.

The overall reaction is a substitution. The result seems the same as the S N reactions
which we studied in Program 19, but the mechanism is different. It is a combination of
the steps of addition and elimination.
Aldehydes and ketones do not react in acyl substitution. This is because they do not
have a good leaving group for the elimination step. Instead, they have only very poor
leaving group options of hydride or a carbanion.

Try to draw the sequence for the reaction of an ester with ammonia.

B The ester is the acyl derivative, and ammonia is the nucleophile. The substitution
reaction gives an amide. You should have drawn something like the following:

These reactions move forward because of the stability of the product relative to the
substrate. The direction of reaction direction is controlled by the strength of the
nucleophile and the quality of the leaving group. This gives the general order of acyl
derivative reactivity as: acyl halide > acid anhydride > ester > acid > amide.

Q 7.6 Draw structural formulae for the following acyl derivatives.
(a) Methyl 3-methylbutanoate
(b) Octanonitrile
(c) Phenylacetic anhydride
(d) N -Cyclohexylethamide
Q 7.7 Give structural formulae and the compound class name for the prod-
ucts from treatment of butanoyl chloride, CH 3 CH 2 CH 2 COCl, with the
following reagents.

(a) Water

(b) N,N -Dimethylamine

(c) Lithium ethanoate

(d) Cyclohexanol