Electric and magnetic properties of hexaethynylbenzene

Coupled Hartree—Fock theory is used to compute the magnetizability and nuclear shielding tensors of hexaethynylbenzene (HEB), and to map the electron current density induced by an external magnetic field. The electric quadrupole moment and polarizability are also computed, and compared with those of benzene and ethyne. The calculations of magnetic properties demonstrate the clear superiority of distributed-origin methods over the conventional common-origin method in which a single fixed origin of vector potential is used. It is shown that the CTOCD-PZ2 formulation provides an efficient and accurate method for the magnetic properties. The current-density maps of HEB show the characteristic π ring current associated with the delocalization of π electrons around the central ring of carbons and local circulations in the ethynyl groups. There is no evidence of a significant induced current linking the ethynyl groups, either through space or through bond. The experimental shielding constants of HEB are well reproduced by the CTOCD-PZ2 calculations, and an analysis of the computed shielding tensors is used to provide a detailed interpretation of the NMR spectrum.