Proton chemical shifts and electron densities in aromatic and heteroaromatic molecules. II. Derivatives of pyrrole and furan

Abstract

In this paper, the methods outlined in Part I are used to estimate the electron distribution from the proton chemical shifts in a series of five-membered ring heteroaromatic compounds. The systems studied are pyrrole and furan, their benzo and dibenzo derivatives, indazole, indolizine, the azaindolizines, and purine. It is found that the estimated excess charges are not as closely represented by the BJ VESCF method as was the case for the azine derivatives and that the role of the σ-electrons is in urgent need of closer investigation.