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.
Dedicated to Academician of the Russian Academy of Sciences M. G. Voronkov in honor of his 85th birthday.
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Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1671–1681, November, 2006. |