Calculation of structures and bond dissociation energies of radical cations: the importance of through-bond delocalization in bibenzylic systems

Abstract

Structures ad energies ({Delta}H{degree}{sub f}) of radical cations and their radical and cationic fragments have been calculated by use of AM1 semiempirical molecular orbital theory and compared with experimental data in the literature. Experimental {Delta}H{degree}{sub f} correlate linearly with calculated heats giving nonzero intercepts and nonunit slopes. The best correlations as judged by the variance of the fit are obtained when performed according to structure types, i.e., aromatic radical cations, alkane radical cations, radicals, and cations. These correlations enable corrections to AM1 values that allow prediction of experimental {Delta}H{degree}{sub f} with uncertainties that approach experimental uncertainties. Used in this way, AM1 can augment experimental thermochemical data and enable confident predictions of reaction enthalpies. Bibenzylic radical cations are calculated to have charge and sin localized in only one of the aromatic rings ether through space or through the ethylenic bond are found.