Molecular‐orbital calculations on electrophilic substitution and relative basicities in pyrrole, indole, furan, and benzofuran

Two molecular‐orbital methods—extended Hückel theory and CNDO/2—have been used to estimate the relative electrophilic reactivities of the alpha and beta positions in the nonalternant heterocyclic compounds pyrrole, indole, furan, and benzofuran by comparing total transition‐state energies. The order of basicities of three positions of indole and pyrrole are predicted. Charge densities are also calculated and evaluated in the light of n.m.r. chemical shift data.