Radical stabilization energy as a measure of the spectral properties and reactivity trends in homologous groups

The existence of linear relationships has been demonstrated between stretching frequencies of R-H, RO-H, CH3CON(R)-H and R-OX (X = H for alcohols and O for peroxy radicals) bonds and radical stabilization energies, E-s(R-.), of related radicals. The correlation equations of E-s(R-.) and R-H bond dissociation energies (BDE), D(R-H), with the above stretching frequencies were obtained. From the equations the D(R-H) values for different hydrocarbons were calculated and compared with the experimental data. The mean difference between calculated and experimental values for saturated hydrocarbons is 2.3 kJ mol(-1). The greater differences for some unsaturated hydrocarbons are discussed and explained. The BDEs calculated from the D(R-H =f(v) equations may be regarded as the best. The IR spectra of menthol, menadione, 3-methylpent-2-en-4-yn-1-ol and retinol were recorded in solution and the E-s(R-.) values of the corresponding radicals and the D(R-H) values of the related C-H bonds in the parent hydrocarbons were estimated for the first time. It is also shown that the radical stabilization energy may be used to estimate the reactivity of organic compounds in free radical reactions. One may conclude that the stabilization energy of the radicals of many organic compounds could be estimated from the vibrational spectra. The E-s(R-.) itself is a useful quantity for predicting kinetic and spectral properties of organic compounds. Copyright (C) 2001 John Wiley & Sons, Ltd.