Kinetics of 1,6-hydrogen migration in alkyl radical reaction class

The kinetics of the 1,6-intramolecular hydrogen migration in the alkyl radical reaction class has been studied using the reaction class transition state theory (RC-TST) combined with the linear energy relationship (LER) and the barrier height grouping (BHG) approach. The RC-TST/LER, where only reaction energy is needed, and RC-TST/BHG, where no other information is needed, are found to be promising methods for predicting rate constants for any reaction in the 1,6-intramolecular H migration in alkyl radicals reaction class. Direct comparison with available experimental data indicates that the RC-TST/LER, where only reaction energy is needed, can predict rate constants for any reaction in this reaction class with satisfactory accuracy

Intramolecular hydrogen transfer reactions of thiyl radicals from glutathione: formation of carbon-centered radical at Glu, Cys and Gly

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemical Research in Toxicology, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/tx3000494Glutathione thiyl radicals (GS•) were generated in H2O and D2O by either exposure of GSH to AAPH#, photoirradiation of GSH in the presence of acetone, or photoirradiation of GSSG. Detailed interpretation of the fragmentation pathways of deuterated GSH and GSH-derivatives during mass spectrometry analysis allowed us to demonstrate that reversible intramolecular H-atom transfer reactions between GS• and C-H bonds at Cys[αC], Cys[βC], and Gly[αC] are possible

Mechanism of the 1-C4H9+O reaction and the kinetics of the intermediate 1-C4H9O radical

The 1-C4H9 + O reaction has been investigated in two quasi-static reactors with different detection systems. From a time-resolved measurement of OH formation by laser induced fluorescence (T = 295 K, p = 21 mbar, bath gas: He) an inverted vibrational state distribution for OH X (2)Pi (v = 0, 1, 2) was observed. By using Fourier transform infrared spectroscopy, relative product yields of 0.55 +/- 0.08 for 1-C4H8, 0.397 +/- 0.05 for HCHO and 0.053 +/- 0.02 for C3H7CHO were determined (T = 298 K, p = 2 mbar, bath gas: He). The results are explained in terms of the formation and subsequent decomposition of an intermediate chemically activated 1-C4H9O radical and a competing abstraction channel leading directly to OH + 1-C4H8. A modeling by statistical rate theory based on ab initio results for the stationary points of the potential energy surface of C4H9O allows the quantitative description of the product branching ratios. From this modeling, threshold energies of E-06 = 55 +/- 6 and E-07 = 88 +/- 6 kJ mol(-1) for the beta -C-C and the beta -C-H bond dissociation, respectively, in 1-C4H9O are obtained. For the 1,5 H atom shift, a most probable value of E-05 = 40 +/- 5 kJ mol(-1) follows from a comparison of our quantum chemical results with data from the literature

Ab Initio Barrier Heights and Branching Ratios of Isomerization Reactions of a Branched Alkyl Radical

The factors influencing the rate of isomerization of alkyl radicals is investigated using ab initio calculations on the example of the 2-methylhexyl radical. The equilibrium geometries of the isomers and the transition structures of 16 isomerization channels connecting them are determined at the UHF/6-31G* level. The isomerization energies and barrier heights are calculated at the MP-SAC2/6-311G** level. The most stable isomer is the tertiary radical, less stable are the secondary isomers, and the least stable are the primary isomers of the 2-methylhexyl radical, the largest energy difference being about 3.5 kcal mol-1. The heights of the barriers separating the isomers depend on the relative location of the radical center before and after the reaction. The barrier height for 1,2 as well as 1,3 H atom transfer is about 37−40 kcal mol-1, that for the 1,4, 1,5, and 1,6 isomerizations is lower, about 20, 13, and 15 kcal mol-1, respectively. The height of the barrier, and, accordingly, the activation energy vary by about 2 or 3 kcal mol-1 depending on the substitution in the ring of the cyclic transition structure and the concomitant change of the reaction enthalpy. Our RRKM calculations show that the fastest isomerization reaction is the 1,5 H atom transfer taking place through a six-membered cyclic transition structure. The relative importance of 1,4 and 1,6 H atom transfers to that of 1,5 isomerization, however, being dependent on the pressure and temperature, may not be negligible, and they together may exceed 30%