THE QUANTUM-CHEMICAL ANALYSIS OF STEREOCH EMICAL EFFECTS IN THE SYSTEM OF 2-VINYLPYRIDINE METHYLPICOLYL MAGNESIUM

Various structures of one- and two-unit adducts of 2-vinylpyridine and methylpicolyl magnesium were studied by quantum-chemical calculations . The second reactant is used as a model of benzylpicolyl magnesium th at yields poly(2-vinyl pyridine) with high content of isotactic sequen ces. The calculations with MNDO method showed that conformations of th e compounds studied are governed by the donor-acceptor interactions of magnesium atom with all the pyridine cycles of an adduct, the picolyl group of initiator included. The mesomorphic form of the two-unit add uct was found to be energetically favorable (20.7 kJ/mol below the rac emic form). This qualitatively agrees with the known experimental obse rvations on the system of 2-vinylpyridine-benzylpicolyl magnesium. The results of the calculations were used to clarify the interpretation o f the mechanism of stereoregularity in this system previously proposed in the literature.