ab initio calculations of the electronic effects in chloropyrimidines and chloropyrazines

RHF/6-31G(d) calculations for 2- and 5-chloropyrimidines and 2-chloropyrazine show alternation of charge and -electron density on the ring atoms in the pyrimidine derivatives and absence of such alternation in the pyrazine derivative. This finding is in accord with bond polarization by the charge of the geminal atom directly through space. The³⁵Cl NQR frequencies estimated from the calculation data for these molecules were similar to the experimental values.Institute of Technical Chemistry, Urals Branch of the Russian Academy of Sciences, 61400 Perm, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 782–785, June, 1999.