STRUCTURAL STUDIES BY NUCLEAR MAGNETIC RESONANCE .19. N,N-DIMETHYLHYDRAZONES AND GENERAL COMMENTS ON CONFIGURATIONAL AND CONFORMATIONAL ISOMERISM

Configurations and conformations were assigned to several aldehyde and ketone N,N-dimethyldrazones from analyses of their 60-Mc NMR spectra. Aldehyde, but not ketone, N,N-dimethylhydrazones exist exclusively in the syn configuration. Interpretation of the vicinal spin-spin coupling constants, JH1Hα, led to the conclusion that II and III are the minimum energy conformations of these compounds. The ΔH0 values for II ⇋ III were found to be more positive than those of N-Me imines (Z = Me) but less positive than those of oximes (Z = OH) and their O-methyl ethers (Z = Me). General comments are made on several aspects of configurational and conformational isomerism about single, double and partial double bonds, and on the usefulness and limitations of NMR in studying various problems associated with such isomerism. © 1968.