Electron spin resonance studies. Part XXXIII. Evidence for heterolytic and homolytic transformations of radicals from 1,2-diols and related compounds

Abstract

The reactions of the hydroxyl radical with a number of compounds containing the unit –CHX–CHY–, where X = OH or OMe and Y = OH, OAc, Halogen, or a protonated amino-group, have been studied by e.s.r. spectroscopy. The transient species involved have been identified on the basis of their hyperfine splittings and g-factors; in the case of the radical ·CH(OH)·CH₂NH₃⁺ and its derivatives, clear trends in the proton and nitrogen nitrogen splittings are observed as the NH hydrogen atoms are successively replaced by methyl groups, and these have been rationalised in terms of an interaction involving both hydroxy- and amino-substituents.

The data not only support the view that radicals containing the fragment –Ċ(OH)–C(OH)[graphic omitted] undergo acid-catalysed elimination of water but also reveal further details of this reaction and information about related heterolytic processes; for example, there is evidence that the radical cation MeOCH–ĊH₂ is formed transiently from the radical ·CH(OMe)·CH₂X (X = Cl or OAc). Amines do not appear to fragment heterolytically from radicals of the type ·CH(OH)·CH₂NR₃⁺, but the formation of the species Me₃N·⁺ from the choline cation suggests that the C–N bond in the species ·CH(OH)·CH₂NMe₃⁺ readily undergoes homolysis.