Bond orders in heteroaromatic rings

Bond orders are calculated at the Hartree-Fock and second-order, Moller-Plesset (MP2) level for 324 distinct ring bonds in 60 heterocyclic molecules. These include benzene and 12 azines, pyrrole and 9 azoles, furan and 9 oxazoles, thiophene and 8 thiazoles, boroxine, trioxadiborole, borazine and 9 azaborinines, 3 azaboroles, and 3 oxazaboroles. The correlated bond orders are generally, but not always, smaller than their Hartree-Fock counterparts. Gordy bond orders differ from the ab initio ones by large amounts. A plot of MP2 bond orders versus bond lengths shows clearly that an empirical Gordy-type relationship cannot be very accurate. Some trends in bond orders are identified. (C) 2002 Wiley Periodicals, Inc.