The asymmetry parameter of the deuteron quadrupole coupling constant in aromatic molecules; σ-π inequivalence

A simple calculation has been made of the quadrupole coupling constant asymmetry parameter of the deuteron in aromatic hydrocarbons. The source of the asymmetry is the inequivalence between the carbon 2pσ and 2pπ orbitals, that is, their different nuclear screening constants. The calculation shows that the experimental magnitude of η is consistent with σ-π inequivalence found in recent valence theory calculations. Moreover, the sign of η implies that the pπ functions project further from the carbon nucleus than the pσ functions.