ESR Studies on Cation Radicals of Saturated Hydrocarbons

Abstract

The most prominent development in the study of cation radicals by electron spin resonance (esr) during the past 20 years is the detection and the structural study of alkane cation radicals[,]. Although an olefin cation was detected by Ichikawa and Ludwig by the radiolysis of tetramethylethylene(TME) in an inert alkane with an electron scavenger[], detection of alkane cations had been unsuccessful despite many efforts such as irradiation of alkanes at 4 K with or without an electron scavenger[]. As a consequence, alkane cations had been thought to be unstable and decomposed by the instantaneous deprotonation. Nauwelaerts and Ceulemans applied the technique similar to that of Ichikawa to an alkane system and reported the spectrum of “n-C8H18 +”. However, it was too obscure to identify the radical as an alkane cation[]. In 1979, Smith and Symons obtained the esr spectrum of the hexamethylethane cation radical (HME+) as the first example of an alkane cation radical, by the radiolysis of HME in CBr4 or CC14[]. This result was, however, not sufficient to be accepted by the general researcher, although its assignment was supported by the subsequent work by Wang and Williams[] and later by Shida et al. using Freons as the matrices[]. It was the work by Iwasaki and his coworkers on C2H6 + in SF6 at 4 K, published in 1981, that gave a definite proof for the detection of the alkane cation radical with clear information on the structure of it[].