Interaction of the atoms in molecules of pyridine and its derivatives according to the results of ab initio calculations

Abstract

Nonempirical quantum-chemical calculations of pyridine and its 2-, 3-, and 4-X-substituted derivatives (X = F, Cl, Br, Me, and Et) by RHF/6-311G(d) and MP2/6-311G(d) methods indicate an alternation of charges on the atoms of the pyridine ring and of the occupancy of their valence py-orbitals. This is caused by the polarization of bonds under the action of the charges of the atoms geminal to C(n). Bonding molecular orbitals in these molecules, formed as a result of the py-orbitals, occurring in the plane of the pyridine ring, are not an indication (characteristic) of p, π-conjugation between the unshared electron pair of the heteroatom of a substituent X and the π-electron system of the ring. The results of the calculations by these methods did not differ in principle.