22. Carboxylic Acid Derivatives: NAS

In nucleophilic acyl substitution, which of the following best describes the key mechanistic step that distinguishes it from nucleophilic substitution at alkyl halides?

Which of the following is the major product when an acid chloride reacts with ${\mathrm{NH}}_3$ in a nucleophilic acyl substitution reaction?

There are many methods for activating a carboxylic acid in preparation for coupling with an amine. The following method converts the acid to an N-hydroxysuccinimide (NHS) ester.

(b) Propose a mechanism for the reaction shown.

Write the mechanism for the reaction of an amino acid with di-tert-butyl dicarbonate.