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A product and time-resolved kinetic studies provide insight into the role of structural effects on the one-electron oxidation of ring-methoxylated arylethanoic acids.

A laser flash photolysis study is carried out to assess solvent effects on the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. The rearrangement rate constant k decreases by increasing solvent polarity and an excellent correlation with negative slope is obtained between log k and the solvent polarity parameter E(sub T)(super N).

A product and time-resolved kinetic study on the reactivity of tertiary arylcarbinyloxyl radicals bearing alpha-cyclopropyl and alpha-cyclobutyl groups is presented. It is proposed that in the transition state for beta-scission, formation of the C=O double bond is assisted by overlap with the C-C bonding orbitals of the cyclopropane ring.

The reactivity of the phthalimide-N-oxyl radical (PINO) toward the NO-methyl C-H bond of a number of 4-X-substituted N,N-dimethylanilines is investigated. It is found that the PINO is very reactive toward the methyl C-H bond of N,N-dimethylanilines promoting the oxidative N-demethylation of the substrate.

Ketyl radicals with lignin related structures are generated by means of radiation chemical and photochemical techniques. The high reactivity of ketyl radicals with oxygen coupled with the low rates of beta-fragmentation of the same species play an important role in the photoyellowing of lignin containing pulps and papers.

Research has been conducted on the ring-methoxylate diarylmethane and diarylmethanol radical cations. The reactivities and properties of these compounds generated in aqueous solution via pulse and gamma-radiolysis have been investigated and the results of the studies are reported.

Research has been conducted on the ring-substituted cumyloxyl radicals. The spectral properties and beta-scission reactions of these radicals have been investigated via the laser flash photolysis study and the results are reported.

A study was conducted on the decay behavior of 1-(4-methoxyphenyl)-alkanol, (4-MeOC6H4CH(OH)R, R=H, alkyl) radical cations in aqueous solution. It reports on the results of a pulse radiolysis analysis of radical cations generated from 2-, 3-, and 4-(4-methoxyphenyl)-alkanols where the OH group is separated from the aromatic ring by an increasing number of carbon atoms. Among other findings, the intermediacy of an oxyl radical is suggested for the base-catalyzed decay of 3-(4-methoxyphenyl)-propanol radical cation.

The one-electron oxidation of several 1-arylpropanols, 1,2-diarylethanols and some of their methyl ethers by potassium 12-tungstocobaltate(III) in aqueous acetic acid is investigated. The oxidation process is subjected to kinetic and product analysis as well as pulse radiolysis experiments. Results provide additional information on the effects of structure upon the competition between carbon-carbon and carbon-hydrogen bond cleavage and the role of the side-chain OH groups in the cleavage of the carbon-carbon bond.

A study of the kinetics of side-chain oxidation of alpha-substituted 4-methoxytoluenes by K5(CoW12O40).11H2O in AcOH/H2O reveals that the reaction rate is affected by electron transfer and radical cation deprotonation processes. The kinetic examination has facilitated the estimation of values of K and the rate constant for the electron transfer process.

A time-resolved kinetic study is used for analyzing the reactions of the tert-butoxyl (t-Bu[O.sup..]), cumyloxyl (Cum[O.sup..]), and benzyloxyl (Bn[O.sup..]) radicals with alkylferrocenes in solution. The studies have shown that both Bn[O.sup..] and Cum[O.sup..] have reacted with the ferrocene donors with rate constants that are in all cases higher than those measured for t-Bu[O.sup..], wherein the radical is well-localized.

A time-resolved kinetic study is carried out on the reactions of alkoxyl radicals with trialkyl and triaryl phosphites. The alkoxyl radical (cumyloxyl) has reacted with triaryl phosphites [(ArO).sub.3]P to provide phenoxyl radicals, with rate constants that are affected to a limited extent by substitution of the aromatic rings.

The reaction of the benzotriazole N-oxyl radical (BTNO) with a series of 4-X-N,N-dimethylanilines (X = CN, C[F.sub.3], C[O.sub.2]C[H.sub.2]C[H.sub.3], C[H.sub.3], O[C.sub.6][H.sub.5], OC[H.sub.3]) is examined in C[H.sub.3]CN. The results are interpreted based on the electron-transfer mechanism from the N,N-dimethylanilines to the BTNO radical followed by deprotonation of the anilinium radical cation (ET-PT mechanism).

A kinetic study is carried out on one-electron oxidation of a series of substituted ferrocenes by the benzotriazole-N-oxyl radical (BTNO) and of ferrocene (FcH) by a series of ring-substituted benzotriazole-N-oxyl radicals in C[H.sub.3]CN. The relative reactivity of PINO and BTNO radicals have represented a criterium to help in the distinction of ET and HAT reactions promoted by these transients N-oxyl radicals.

Kinetic studies are carried out on one-electron oxidation of a series of ferrocenes by phthalimide-N-oxyl radical (PINO) generated in C[H.sub.3]CN by reaction of N-hydroxyphthalimide (NHPI) with the cumyloxyl radical. The intrinsic reactivity of PINO in electron-transfer reactions is calculated from the Marcus cross relation and self-exchange rates of ferrocene and dimethylferrocene.

The reactivity and acid-base behavior of ring-methoxylated arylalkanoic acid radical cations and radical zwitterions in aqueous solution is investigated through time-resolved studies. The results reveal that the radical cation p[K.sub.a] values increase by increasing the number of methoxy ring substituents and by increasing the distance between the carboxylic group and the aromatic ring.

A product and time-resolved kinetic study on the reactivity of the radical cations generated from cyclopropyl(4-methoxypehnyl)phenylmethanol (1) and cyclopropyl[bis(4-methoxyphenyl)]methanol (2) is carried out in aqueous solution. The product distributions observed in the reactions of 1(super .+) and 2(super .+) are rationalized in terms of a water-induced competition between O-neophyl shift and C-cyclopropyl beta-scission in the intermediate 1,1-diarylalkoxyl radicals 1r(super .) and 2r(super .).

A product and time-resolved kinetic study of the effect of ring substitution on the reactivity of 1,1-diarylalkoxyl radicals are carried out. The radicals undergo an O-neophyl shift to give the isomeric 1-aryl-1-aryloxyalkyl radicals from which the corresponding aromaticketones are formed.

The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl) -2-butoxyl radical are measured directly by laser flash photolysis. The benzocycloalken -1-oxyl radicals undergo ring opening with rates, which parallel the ring strain of the corresponding cycloalkanes.

A steady-state and laser flash photolysis (LFP) study of the 2,4,6-triphenylpyrylium tetrafluoroborate (TPPBF4)-photosensitized oxidation of ring-methoxylated benzyl alcohols is carried out. The evidence on the involvement of intermediate benzyl alcohol radical actions and benzylic cations in the reactions is provided through laser flash photolysis (LFP) experiments.

A systematic product study was conducted for the beta-scission reactions of an extended series of 1-alkylcycloalkoxyl radicals, where both the ring size and the nature of the alkyl group were varied. The results demonstrate that regioselectivity is governed by the release of ring strain associated to ring opening and stability of the alkyl radical formed by C--R cleavage.

The one electron oxidation of ring-dimethoxylated phenylethanoic acids is investigated at different pH values. Findings are discussed in terms of the ease of intramolecular side chain to ring electron transfer required for decarboxylation.

The trap depth of 8-oxo-7,8-dihydro-2' deoxyguanosine derived from electron transfer equilibria in aqueous solution is described.

The reaction of 4-methoxycumyl alcohol (MCA) radical cation in acidic and basic solutions was investigated. The radical cation of MCA was formed by pulse radiolysis in water utilizing SO4*- or Tl2+ as the oxidant. For the first time, direct evidence was acquired indicating that 1-arylkanol radical cations can be deprotonated at the OH group to finally produce a highly reactive alkoxyl radical.

The C-H bond was shown not to affect the hydroxide-induced deprotonation of alpha-hydroxy-substituted alkyl-aromatic radical cations in water for carbon radical formation. The deprotonation of the alpha-OH bond to produce a benzyloxyl radical via a radical zwitterion was suggested to be the step before the intramolecular electron transfer. The benzyloxyl radical product was converted into a carbon radical by a 1,2-hydrogen atom shift.

A product and time-resolved kinetic study on the reactivity of the radical cations generated from cyclopropyl(4-methoxyphenyl)phenylmethanol (1) and cyclopropyl[bis(4-methoxyphenyl)]methanol (2) has been carried out in aqueous solution. In acidic solution, 1·+ and 2·+ display very low reactivities toward fragmentation, consistent with the presence of groups at Cα (aryl and cyclopropyl) that after CαCβ bond cleavage would produce relatively unstable carbon-centered radicals. In basic solution, 1·+ and 2·+ display oxygen acidity, undergoing -OH-induced deprotonation from the α-OH group, leading to the corresponding 1,1-diarylalkoxyl radicals 1r· and 2r·, respectively, as directly observed by time-resolved spectroscopy. The product distributions observed in the reactions of 1·+ and 2-+ under these conditions (cyclopropyl phenyl ketone, cyclopropyl(4-methoxyphenyl) ketone, and 4-methoxybenzophenone from 1·+; cyclopropyl(4-methoxyphenyl) ketone and 4,4′-dimethoxybenzophenone from 2·+) have been rationalized in terms of a water-induced competition between O-neophyl shift and C-cyclopropyl β-scission in the intermediate 1,1-diarylalkoxyl radicals 1r· and 2r·. [ABSTRACT FROM AUTHOR]