Va. Roginsky et al., COMPARATIVE PULSE-RADIOLYSIS STUDIES OF ALKYL-SUBSTITUTED AND METHOXY-SUBSTITUTED SEMIQUINONES FORMED FROM QUINONES AND HYDROQUINONES, Journal of the Chemical Society. Faraday transactions (Print), 94(13), 1998, pp. 1835-1840
Citations number
39
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
Absorption spectra and rate constants for the disproportionation of 12
alkyl- and methoxy-substituted semiquinone anion free radicals (Q(.-)
) produced by the one-electron reduction (using CO2.- as a reductant)
of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation
(using N-3(.) as an oxidant) of the corresponding hydroquinones (QH(2)
) were determined by pulse radiolysis in 50 mM sodium phosphate buffer
, pH 7.40 at room temperature. Both spectral and kinetic characteristi
cs of Q(.-) only moderately depended on whether Q .(-) was produced fr
om Q or QH(2). Spectra of benzosemiquinones display two peaks with max
imum at 310-320 nm and ca. 430 mm with the ratio of about 2-2.5. Molar
absorption coefficients were determined. Rate constants for Q(.-) dis
proportionation (2k(1)) were correlated with the nature of substituent
s. While 2k(1) was scarcely affected by methyl substitution, Q(.-) con
taining isopropyl, tert-butyl and methoxy substituents were visibly mo
re stable than non-substituted and methyl-substituted Q(.-).