Hydrolysis of amides. VI. Dilute acid hydrolysis of N-alkyl substituted acetamides

Abstract

Enthalpies and entropies of activation have been derived from rate constants measured over a range of temperature for the dilute acid hydrolysis of N-methyl- acetamide, N-ethylacetamide, N-n-propylacetamide, N-isopropylacetamide, N-n-butylacetamide, N-s-butylacetamide, N-isobutylacetamide, N-isopentyl-acetamide, N-n-hexylacetamide, N-cyclohexylacetamide, and N-benzylacetamide. An analysis of the rate data in terms of several Taft-type linear free energy relationships indicates that the change in steric environment which a substituent experiences when it is moved from the acyl part to the alkyl part of an amide is quantitatively similar to the change in steric environment experienced by the same substituent in moving from the acyl to the alkyl portion of an ester. Evidence is also presented that the change in six-number makes the greatest contribution to the change in steric environment.