INDO MO calculations of the electronic structures of pyrolle, imidazole, and derivatives

Abstract

INDO MO calculations on a series of N-substituted pyrroles and imidazoles have been analysed for substituent effects. Some of the basic characteristics of the σ I and σ R 0 parameters are reflected in the calculated electron densities of the compounds studied. For example, good correlations are obtained between Δ qσ N(1)/ΣΔ qσ parameters and σ I for the R substituted compounds, as well as between ΣΔ qπ values and σ R 0 for the + R derivatives. The + R substituents lead to an increased localization of the π-bonds, whereas R substituted derivatives show an increased delocalization, i.e., the π-bond orders across C(2)C(3) [or C(2)N(3)] and C(4)C(5) decrease and those across other bonds in the ring increase.