PREDICTION OF PREFERRED PROTONATION SITES IN PYRROLE AND ITS METHYL-DERIVATIVES USING MOLECULAR ELECTROSTATIC POTENTIALS DERIVED FROM THE PM3 AND AM1 METHODS
Y. Nakajima et al., PREDICTION OF PREFERRED PROTONATION SITES IN PYRROLE AND ITS METHYL-DERIVATIVES USING MOLECULAR ELECTROSTATIC POTENTIALS DERIVED FROM THE PM3 AND AM1 METHODS, Journal of molecular structure. Theochem, 107(3), 1993, pp. 199-205
The PM3 and AMI molecular orbital programs have been employed for the
investigation of the preferred protonation sites in pyrrole and its N-
methyl, 2,5-dimethyl, 3-methyl, 2-methyl and 1,2-dimethyl derivatives.
The following are reported: the LCAO coefficients of the HOMO (2p(z))
(the HOMO coefficients); the atomic centered charges, which are calcu
lated by the subroutine ''ESP'' (ESP charges); the atomic net charges,
which are obtained by a Mulliken population analysis (Mulliken net at
omic charges). The predictions of the preferred protonation sites made
by the HOMO coefficients and ESP charges are in perfect agreement wit
h experimental data, whereas those made by the HOMO coefficients and M
ulliken net atomic charges are not in agreement. It is hence obvious t
hat the protonation of pyrrole and its methyl derivatives is controlle
d by not only HOMO-LUMO interaction but also by electrostatic forces,
which are estimated by ESP charges. In other words, the subroutine ''E
SP'' is useful for estimation of a kind of electrostatic reaction of p
yrrole and its methyl derivatives, which suggests that the subroutine
may be effective for the investigation of the electrostatic reactions
of other compounds.