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.
