Protonation acidity constants for some benzamides, acetamides, and lactams

Abstract

Protonation acidity constants for 27 benzamides, acetamides, and lactams have been determined. Ultraviolet, and 13C and 1H nmr, spectroscopic methods were used; almost all the spectra were found to be subject to medium effects, some quite severe, as the sulfuric acid concentration was increased. Despite this, the excess acidity (X-function) method gave accurate [Formula: see text] and m* values. In all cases protonation, followed by a medium shift in the spectrum of the protonated form, was the only process taking place; protonation was essentially complete in 60% H2SO4. The results for the different bases are interpreted in terms of the resonance, inductive, and steric effects in operation in the acid and base forms.