Abstract
The molecule N,N‐dimethylacetoacetamide, which is subject to a keto–enol equilibrium process in solution, also exhibits hindered rotation about the amido NC bond. The hindered rotation rates have been studied by lineshape fit methods of the nuclear magnetic resonance spectra. In spite of some overlap of the keto and enol N‐methyl proton signals, the simultaneous measurement of the two distinct energy barriers in the two forms is possible as well as a determination of the keto–enol equilibrium. The differences in free energy of activation between keto and enol forms for the rotation barrier can be related to the conjugation energy of the NC π system with the enolic hydrogen bonded ring. Appeal to the model compound acetylacetone reveals a consistent set of energies for the keto and enol forms in the ground and transition states for internal rotation. The opportunity has been taken to reexamine and compare the keto–enol system ethylacetoacetate. Long range, solvent, concentration and temperature sensitive scalar couplings ^4^J(HH) between the enolic –OH and the adjacent methyl group in acetoacetic ester have not hitherto been reported.