Effects of diffusion on the self‐termination kinetics of isopropylol radicals in solution

Abstract

Rate constants for the bimolecular self-reaction of isopropylol radicals [(CH&COH] in various solvents are determined as functions of temperature by kinetic electron spin resonance. For hydrocarbon solvents they are well described by theoretical equations for reactions controlled by translational diffusion if diffusion coefficients of 2-propanol, a constant reaction distance, and a spin statistical factor of ' /4 are applied. Deviations from 2kt -D a t high diffusion constants agree with trends expected from recent theoretical models. For hydrogenbonding solvents large negative deviations are observed. They are attributed to steric constraints and slower rotational diffusion of radical-solvent aggregates. The disproportionation-to-combination ratio of isopropylol increases with solvent viscosity. As previously for tert-butyl, this is explained by anisotropic reorientation during encounters. Further, rate data are given for the decarbonylation of the 2-hydroxy-2-methylpropanoyl radical and for several hydrogen abstraction reactions of isopropylol.

Triplet and reversed triplet mechanism CIDEP studied by quenching experiments

“…It is assumed that initially v = 0 and M z = Reasonable values for many of the parameters may be obtained from the literature, which for the experimental conditions used are, 2k t = 4. 10 9 M-1s -1 [25], T 1 ~ T 2 ~ 0.8 gs [12], co l = 4.6.105 rad. s -1 [24], Peq --250 V. M -1 [24] and PF = 3PG = 30 for acetone [12,26] and PF = 2Po = 30 for benzophenone.…”

Rate constants for the decarboxylation of the t‐butoxicarbonyl radical and concurring radical terminations directly obtained by kinetic ESR

“…However, Eqs. (13) and (14) imply that kl is obtainable without knowledge of c2 which, as was mentioned above, makes the method particularly attractive for the determination of unimolecular or pseudo first-order processes.…”

“…To this end r2 in Eqs. (13) and (14) was replaced by s2 which is correct. rl was initially approximated by s,, and Eq.…”

Time resolved ESR study of the oxidation of the ascorbic Acid/Ascorbate system by the isopropylol radical in aqueous solution

“…The acyl species decarbonylates within 2 ~s [22]. This provides a second isopropylol radical on a time scale which is short compared with the reactions of interest, in the presense of Ha/k/HA-, N zwas observed asa secondary radical with no further paramagnetic species of detectable concentration.…”

“…The rate equations for the concentrations of the radicals (CH3)2COH (abbreviated as R-) and A-become: The stmctures and ESR spectra of both radicals are well known [22,23]. Ala intense, non-oveflapping line of each species was chosen for kinetic measurements.…”