Variable temperature 1H NMR lineshape analyses and 13C NMR spin-lattice relaxation time studies were undertaken to characterise the conformationally dynamic N-alkyl 1- and 2-benzazepinones 1 and 2. For 1, dynamic interchange between two mirror-image puckered forms of the azepine ring occurs with a barrier of 56 kJ mol-1. There is a significantly greater degree of ring flexibility in the case of 2. Molecular modelling studies were used to examine the degree of sidechain flexibility in these compounds.