MNDO method was applied to the study of the regio-selectivity of mercuration of N-(benzylidene) aniline, N-(benzylidene)-2-toluidine and N-(4- nitrobenzylidene)-2-methoxy-aniline. The results obtained disclosed that the electron densities on the N-phenyl ring in the stable conformations are larger than those on the C-phenyl ring. Therefore, the mercuration occurs in N-phenyl ring rather than in C-phenyl ring. The electron population on the imino-nitrogen atom is the largest, thus the mercuric acetate shoud first coordinate with imino-nitrogen atom in the process of the reaction and then subsequent electrophilic substitution takes place in the ortho-position of the N-phenyl ring. However, in the stable conformation of N-(benzylidene)-2-toluidine, the o-methyl group blocks the way of the imino-nitrogen atom to coordinate with mercuric acetate, the mercury atom can not be directed into the ortho-position of the N-phenyl ring and thus only para-mercuration product is formed. The calculated results are consistent with those of the experimental and further support the mechanism proposed previously.

Key words: REGIOSELECTIVITY