1H and 13C NMR studies of para-substituted benzaldoximes for evaluation of the electron donor properties of substituted amino groups

H-1 and C-13 NMR spectra of seventeen (E)-benzaldoximes and three acetophenone oximes, both carrying substituted p-amino groups, have been recorded and discussed from the point of view of substituent effect, The resonance effect of these substituents is not transmitted strongly to CH=NOH group, However, it is found that the chemical shift of C-para depends linearly on sigma(R) degrees values. This dependence has been used to calculate the resonance substituent constants for the less common amino groups and the 1-pyrrolidine group is found to be the most powerful electron donor among the substituents studied.