Characterization of Equatorial and Axial Six-Membered-Ring Peroxyl Radicals

Abstract

Spectroscopic data are consistent with computations that show that, in their most stable conformations, the peroxyl moiety is equatorial in cyclohexylperoxyl radicals and axial in oxa- and most polyoxacyclohexyl-2-peroxyl radicals.

Observation of the Ã−X̃ Electronic Transitions of Cyclopentyl and Cyclohexyl Peroxy Radicals via Cavity Ringdown Spectroscopy

“…±45°. The latter types (dubbed “gauche” in this study, vide infra) were predicted to be more stable than the former (“cis”) forms …”

“…Previous experimental efforts have already yielded the B̃−X̃ absorption spectra of cyclopentyl , and cyclohexyl ,, peroxies, both of which consist of broad, featureless absorptions centered around 250 nm with widths (fwhm) of ∼40 nm. Cyclopentyl and cyclohexyl , peroxies have also been investigated via solution-phase EPR spectroscopy, the latter most recently by DiLabio, Ingold, and Walton (DIW), who attempted to observe distinct EPR signals for the axial and equatorial conformers . Although their calculations predicted that the most stable axial and equatorial forms of cyclohexyl peroxy are close in energy, DIW were able to observe only one signal, probably due to similar hyperfine parameters for the two species.…”

DFT calculations of the anomeric and exo-anomeric effect of the hydroperoxy and peroxy groups

“…1) but are rather similar to energy profiles calculated for peroxy radicals. 21 In the case of radicals, however, the calculated rotational barriers are lower and the minimum at the gg conformer is less pronounced compared to peroxy anions. The energy profiles also differ from energy profiles calculated for 2-methoxytetrahydropyran, 5,8 yet are surprisingly similar to profiles calculated for 2-methylammoniotetrahydropyranyl cation.…”

“…The B3LYP/6-311++G ** calculated geometrical parameters and the relative energy (kcal/mol) for the axially and equatorially oriented hydroperoxy and peroxy substituted saccharide derivatives (1-4, 21, and 22) Compound are considerably higher than those calculated for THX derivatives and for peroxy radicals. 21 This can be ascribed to the abovementioned electrostatic repulsion. For both anomeric forms of THP (17A, 18A), the calculations in a vacuum predict an approximately threefold symmetry for torsional potential with minima at the staggered conformation.…”

Electron spin resonance

“…For the oxacyclohexylperoxyl radicals it is thought that the axial isomers are the most stable, in consequence of the anomeric effect. 102 When 2,2,3,3-tetramethylmethylenecyclopropane is exposed to g-radiation in a solid Freon matrix or to X-rays as isolated in an argon matrix, the resulting radical cation readily ring-opens to form the 1,1,2,2-tetramethyltrimethylene methane radical cation (5).…”