Evaluation of electron-donor properties of amides and lactams by C-13 NMR spectroscopy

The relative basicity of a series of amides and lactams was evaluated in th e C-13 NMR scale by the change in the chemical shift of the carbonyl carbon signal on deuteronation. The effect of the electronic structure of substit uents on the electron-donor properties of the carbonyl oxygen atom was anal yzed. The sterically strained ring in lactams and hydrocarbon substituents at the nitrogen atom increase the contribution of the N-deuteronated form t o the acid-base equilibrium.