Ring currents and magnetic properties of pyracylene

A distributed-origin coupled Hartree-Fock method is used to compute the current density induced in the pyracylene (cyclopent[fg]acenaphthylene) molecule by an external magnetic field, and hence to plot the π ring currents and obtain ab initio values of the total magnetisability, 13C and 1H nuclear magnetic shieldings. The calculated map shows paramagnetic ring currents over the pentagons and diamagnetic circulation around the central naphthalenoid unit of pyracylene, and accounts semi-quantitatively for the measured difference in chemical shift between protons attached to the pentagons and hexagons of this molecule.