STEREOCHEMICAL AND ELECTRONIC INTERACTION STUDIES OF ALPHA-HETEROSUBSTITUTED ACETONE OXIMES

The free nu(C=N) bands in the IR spectra of some alpha-heterosubstituted acetone oximes show the existence of only a monomeric form in chloroform solutions at concentrations below 10(-2) M, while in carbon tetrachloride self-associated species are also present. The H-1 and C-13 NMR chemical shift data indicate the predominance of the E over the Z isomer. The Delta nu(C=N), frequency shifts and molecular mechanics calculations strongly suggest that the oximes are in the gauche conformation. X-ray diffraction data have shown that the single dimethylaminoacetone oxime isomer exists in the E configuration and gauche conformation. Non-additivity effects for the ir-methylene carbon chemical shifts seem to indicate the occurrence of a pi(C=N)/sigma(C-X)* interaction besides the pi(C=N)*/sigma(C-X) hyperconjugative interaction.