Structures and Reactions of Radical Cations of Linear Alkanes: ESR Evidence for Selective Deprotonation

Article abstract of DOI:10.1021/j100284a026

It has been shown that the linear alkane radical cations (C4-C7) radiolytically produced in SF6 at 77 K exhibit the planar extended structure with no detectable gauche conformers.The two in-plane C-H bonds at the chain end preferentially participate in the ? delocalized molecular orbital resulting in higher unpaired electron density as compared with that of the out-of-plane C-H bonds.Upon warming above 100 K, all the linear alkane radical cations in SF6 exclusively undergo selective deprotonation from the chain end to form 1-alkyl radicals, as is expected from the unpaired electron distributions.The results are consistent with our recent observation of the selective formation of 1-alkyl radicals in the 4 K radiolysis of neat crystalline linear alkanes.Formation of 2-alkyl radicals previously observed in CFCl2CF2Cl is reasonably ascribable to the reaction via the gauche at C2 conformation, in which the unpaired electron is highly populated in the in-plane C-H bond at C2 rather than the chain end.The present paper provides further support for our correct interpretation recently given for the reversible temperature change of the spectrum of n-butane radical cations and clarifies the confusing argument made by Lund and his co-workers on the structure and reactions of the alkane radical cations.