Fragmentation reactions of radical cations

Abstract

This paper summarizes most of the recent work by our group on the kinetic aspects of a variety of fragmentation reactions of radical cations involving the cleavage of C-H, O-H, C-C, and C-S bonds. In particular, the problems that have been addressed concern: (a) the carbon acidity/oxygen acidity dichotomy in the fragmentation of aryl- and thioarylalkanol radical cations; (b) the decarboxylation of aryl and thioarylacetic acid radical cations; (c) the structural factors influencing the rate of C-S bond cleavage in the radical cations of phenyl alkyl sulfides. The results presented and discussed have allowed us to recognize the important role played by the electron reorganization energy, associated with the intramolecular electron transfer from the scissile bond to the SOMO, with respect to the dynamics and mechanism of the fragmentation process in the radical cation. Copyright (c) 2006 John Wiley & Sons, Ltd

Kinetics of C–C and C–H Bond Cleavage in Phenyl Alkane Radical Cations Generated by Photoinduced Electron Transfer

“…For the most efficient overlap between these orbitals that would facilitate the electron transfer, the σ bond should be in a perpendicular orientation with respect to the plane of the phenyl rings. 4,94 The σ-bond cleavage kinetics of a radical cation would be relatively slow if its most stable conformation does not correspond to the favorable conformation for the σ-bond/π-system overlap. 4,94 In order to shed light on these structural aspects, we have undertaken 95 a computational study of the structures and energetics of the phenyl alkane radical cations.…”

“…4,94 The σ-bond cleavage kinetics of a radical cation would be relatively slow if its most stable conformation does not correspond to the favorable conformation for the σ-bond/π-system overlap. 4,94 In order to shed light on these structural aspects, we have undertaken 95 a computational study of the structures and energetics of the phenyl alkane radical cations. Our preliminary results from DFT/UB3LYP/6-31g-full optimization calculations (solvent: acetonitrile) using Gaussian-09 show that in the most stable conformation of the TPE radical cation the C−C bond in the β position with respect to a phenyl moiety is nearly perpendicular to the plane of the phenyl ring, while in the most favorable case, the β-C−H bond is off from such orientation by nearly 30°.…”

Review Article: The Effects of Radiation Chemistry on Solvent Extraction: 1. Conditions in Acidic Solution and a Review of TBP Radiolysis

“…in aqueous solution involves fragmentation via C-H bond cleavage to produce a carbon-centered radical and a proton: [41] …”

Photoinduced One-Electron Oxidation of Benzyl Methyl Sulfides in Acetonitrile: Time-Resolved Spectroscopic Evidence for a Thionium Ion Intermediate

“…0.9 µs, respectively). 30 On the contrary, the deprotonation rate constant of toluene radical cation (PhCH 3 31 in water is nearly five orders of magnitude higher than that of 4-methoxytoluene (4-CH 3 O-C 6 H 4 -CH 3 32 33 In other words, on the basis of these data it can be stated that for radical cations of such structure the kinetic acidity parallels thermodynamic acidity. In the case of benzyl methyl-and 4-methoxybenzyl methyl sulfide radical cations, the significant amount of spin and positive charge delocalized not only on the ring but also on the sulfur atom (as indicated by DFT calculations), makes weaker the substituent effect.…”