Studies of Primary Alkyl and Aralkyl Radicals Using Electron Spin Resonance Spectroscopy and Intermediate Neglect of Differential Overlap Calculations

Article abstract of DOI:10.1021/j100234a018

It is argued that a published ESR spectrum due to n-propyl radicals in solution does not, as has been claimed, exhibit selective broadening of the lines with M = 0 for the α protons, but, rather, a broadening of the lines with M = +/- 1 for the β protons.Based on INDO calculations for the n-propyl radical, and an analysis of the restricted internal rotation, the reported variations in a_γ with temperature are rationalized.ESR spectra of 2-hydroxyethyl radicals in solution have been analyzed, and no line width alternation was detected at temperatures of -50 deg C and above.The well-known line width alternation in the ESR spectrum on n-butyl radicals is discussed and it is suggested, partly on the basis of INDO calculations, that the preferred orientations about the C_α-C_β bond are dependent, to some extent, on the configuration with respect to the C_β-C_γ bond.The ESR spectra of the species Me3CCH2CH2^., Me3CCH2CH2CH2^., and Ph3CCH2CH2^. are reported and discussed.The spectrum of the former species shows no line width alternation, but the spectrum of the latter species shows a pronounced alternation, which is attributed to the chiral nature of the trityl group.ESR spectra of the species Me(CH2)_nCH2^. and Ph(CH2)_nCH2^., with n = 2,3, and 4, display particularly marked line width alternation in the latter series when n = 3 and 4.This observation, together with the results of INDO calculations, may possibly indicate that these radicals prefer conformations with the plane of the trigonal carbon atom parallel to the phenyl-group plane.