H-atom abstraction from thiols by C-centered radicals. A theoretical and experimental study of reaction rates

Abstract

The Arrhenius parameters and rates of reaction of three hydroxyradicals, methyl radical, and the hindered primary C- centred radical from t-butyl alcohol with dithiothreitol were measured by pulse radiolysis in water. The bimolecular rate constants were found to be in the order: C-.(CH3)(2)OH > (CH)- C-.(CH3)OH > (CH2OH)-C-. > (.)CH3 > (CH2C)-C-.(CH3)(2)OH. The reaction of three of these, C-.(CH3)(2)OH, (CH2OH)-C-., and (CH3)-C-., with methanethiol were examined at the ab initio B3LYP/6311+G(d,p) level, coupled with transition state theory, both in the gas phase and in solution. The solvent effects are evaluated by two different continuum models (SCIPCM, CPCM), coupled with a novel approach to the calculation of the solution phase entropy. The reaction is discussed in terms of the charge and spin polarization in the transition state, as determined by AIM analysis, and in terms of orbital interaction theory. Rate constants, calculated by transition state theory are in good agreement with the experimental data

Direct bonding between poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) and rubber with radicals

“…It can be estimated that the bonding was caused by a radical reaction and focused on possibilities of hydrogen abstraction reactions18, 19 between radicals from vulcanization agents and thermoplastics polymers.…”

Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

“…For several series of similar hydrogen abstraction reactions where steric hindrance increases, reductions in A of two or three orders of magnitude have been reported in both experimental and computational studies. [47][48][49][50] Within the range of experimental error, there is little difference in E A between BA and BMA, suggesting that there is little difference in the structure of the transition states of the two chain transfer reactions.…”

Cysteine residues as catalysts for covalent peptide and protein modification: a role for thiyl radicals?

“…Considering the significantly lower BDEs of the α C-H bonds of amino acid residues compared to the C-H bonds of alcohols and ethers, the similar rate constants suggest that hydrogen transfer reactions by thiyl radicals are not controlled by thermodynamics alone. In fact, polar effects promote the reactions of thiyl radicals with alcohols and ethers [10, 24], but may be of lower significance for the reactions of thiyl radicals with amino acid residues in peptides. It has been concluded that the α C-H bonds of amino acid residues are deactivated by inductive effects, especially in reactions with highly oxidizing radicals such as the hydroxyl radical (HO • ) and chlorine radical (Cl • ), but such inductive effects are less likely to control the reactions of less oxidizing radicals (such as thiyl radicals) [25].…”