MNDO (Modified Neglect of Diatomic Overlap) Study of the Nucleophilic Substitution Reactions of Chloropyrimidines

In the case of the reaction of 2, 4-dichloro-6-R-pyrimidines with methoxide anion, in which R is a methoxycarbonyl, chlorine, hydrogen, phenyl or methyl group, the replacement reaction of a chlorine atom with a methoxy group occurs predominantly at the 4-position, whereas the substitution takes place mainly at the 2-position when R is a methoxy group. The effect of the substituent at the 6-position on the reactivity of the chlorine atom of the chloropyrimidines was studied by using a semiempirical molecular orbital method (MNDO method). It was proved that the reaciton process from the reactants to the Meisenheimer-type complex plays an important role in determining the direction of the progress of the reaction.