Substituent effects on induced current densities in penta- and heptafulvenes

Explicit ring-current maps based on distributed-origin coupled Hartree–Fock calculations are constructed for substituted penta- and heptafulvenes CnHnX (n = 5, 7; X = NH2+, O, NH, CH2, BH2−). The pattern changes from paratropic to diatropic current in the five-membered ring (vice versa for the seven-membered ring) as X changes from strong π electron acceptor to donor. The trend is explained by a new analysis of frontier-orbital contributions that links the currents in these substituted molecules to those in the parent carbocycle.