STUDIES ON THE STRUCTURE AND BETA-BOND SCISSION REACTIONS OF PRIMARY ALKYL RADICALS, CH3(CH2)NCH2(CENTER-DOT), FOR N=1-6

HF/6-31G optimized geometries are reported for n-alkyl radicals from n-propyl to n-octyl in two extended chain conformations, one where the radical carbon 2p orbital housing the unpaired electron is eclipsed t o a beta-CH bond and another where the orbital is eclipsed to a beta-C C bond. In all cases, the beta-CH eclipsed conformer is almost-equal-t o 100-200 cal/mol lower in energy than the beta-CC eclipsed conformer. The geometry at the radical center is nonplanar by approximately 14-d egrees, indicative of some ''s'' character in the carbon 2p orbital co ntaining the unpaired electron. In the radicals studied here, the bond lengths of the eclipsed beta-CH and beta-CC bonds are longer than the corresponding noneclipsed beta-bonds, attributed to a hyperconjugativ e interaction. Potential functions for internal rotation about the alp ha, beta, and gamma bonds reveal the following: rotation about alpha-C C bonds is free but rotation about beta- and gamma-bonds have barriers of almost-equal-to 3 kcal/mol. Bond scissioning and isomerization rea ctions for n-alkyl radicals are calculated and compared with experimen tal data. The DELTAE values, the changes in total energies between pro ducts and reactants, including zero point energies, for C-H rupture ar e of the order of 33 kcal/mol, while for C-C scissioning, DELTAE almos t-equal-to 20 kcal/mol. 1,3-, 1,4- and 1,5-isomerization reactions hav e much lower DELTAE values and, on a relative basis, appear to be the preferred reaction pathway for the radicals.