When acidic solutions of titanous ion and hydrogen peroxide react immediately before passing through the cavity of an electron spin resonance spectrometer, a singlet is observed in the spectrum which is attributed to the hydroxyl radical. The addition of alcohols to the reactants results in the replacement of this signal by the spectra of organic radicals formed by abstraction of a hydrogen atom from a C-H bond or (in one case) by addition to C=C. Analysis of the spectra gives evidence about the structures of the radicals and hence about the course of the reaction.Coupling constants for protons in different environments are reported and discussed.* The stability and resolution of the spectrometer have been greatly improved since our preliminary result was reported.4
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 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 theview that radicalscontaining the fragment-C(0H)-C(OH)< 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 M e k H -t H, is formed transiently from the radical .CH(OMe)-CH,X (X = CI or OAc). Amines do not appear to fragment heterolytically from radicals of the type -CH(OH).CH2NR3+, but the formation of the species Me,"+ from the choline cation suggests that the C-N bond in the species *CH (OH)*CH2NMe3+ readily undergoes homolysis.previously been adduced, from e.s.r. generated by y-irradiation of an aqueous solution of the spectroscopic observations, that when ethylene glycol is oxidised with the hydroxyl radical [from the titanium-(111) ion-hydrogen peroxide system or photolysis of hydrogen peroxide 3], the first-formed radical (1) undergoes dehydration to give the radical (2) in an acidcatalysed reaction (i).2,3 A number of related transformations has been documented,2 and support for the occurrence of reaction (i) has subsequently been obtained from an investigation in which the radical (1) was
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.