Theoretical a b i n i t i o and low-temperature ESR study of the cyclohexane cation

Abstract

The cyclohexane cation has been studied theoretically using ab initio MO-LCAO-UHF calculations, as well as experimentally, by means of low-temperature ESR measurements in a CF3CCl3 matrix between 4 and 140 K. It is found that the most stable conformation of the free cation is a distorted chair conformation with Cs symmetry, with one carbon atom being separated from the others by bonds that are approximately 0.1 Å larger than the remaining C–C bonds. The symmetrical chair conformation of C2h symmetry is predicted by the calculations to lie approximately 6 kcal/mol above this lowest state. The possibility of a change of ground state because of matrix interactions is discussed in connection with the temperature dependence of the spectra.

Conformers, electronic states, and diabolical conical intersections in the valence photoelectron spectroscopy of halocyclohexanes

“…Focusing on the former picture, the non-degenerate A ′ and A ′′ states arise from a degenerate pair of eg molecular orbitals in cyclohexane by symmetry breaking due to the halogen substituent and the interaction of the ring with the halogen lone pair, which is reminiscent of Jahn-Teller coupling in the cyclohexane cation. 71 In C S symmetry, the p-type halogen lone pair electron hole in the cation may either be symmetric or antisymmetric, i.e., aligned perpendicular to or parallel with the C 6 ring. This is also clearly seen in the Dyson orbitals in Fig.…”

MARY and Optically Detected ESR Spectroscopy of Radical Cations ofcis-andtrans-Decalin in Nonpolar Solutions

“…Since in Freon the cis and trans isomers give similar ESR spectra at nitrogen temperatures, the dramatic difference observed in their OD ESR spectra in alkane matrices deserves special consideration. It is well-known that in radical cations of many cyclic alkanes (e.g., cyclohexane) the intramolecular dynamic transitions between degenerate Jahn−Teller states can take place. ,, The latter leads to the modulation of hyperfine coupling constants, which should reveal itself in the OD ESR spectra. It is believed that a strong anisotropy and large shift of g -factor, typical of these Jahn−Teller active radical cations, result from the admixture of orbital state, which also shortens the spin−lattice relaxation times.…”

Electron spin relaxation of some alkane cation radicals as an indicator of dynamics between the distorted structures

“…It should be remarked that there is no reason for the three distorted structures to have an equal potential energy in the frozen matrix, thus an nonequivalent averaging naturally occurs, which yields three sets of hyperfine couplings instead of two sets expected for the cation with C2h symmetry. This interpretation is reasonably extended to the cation in Fil before annealing as well as to that in CF3CCI 3 [11], and gives confirmation that these cyclohexane cations have a C2h structure induced by JT distortion for the system without dynamics [9].…”

“…It has been revealed that cyclohexane cation in frozen matrices has an elongated chair forra (C2h) with the unpaired electron in ag orbital ( Fig. la), which is derived from a regular chair form of D3d due to JT distortion [9][10][11]. The observed hyperfine structure was attributed to the three pairs of equatorial protons (hyperfine structure constants (hfc's) are 8.5, 3.4, and 1.4 mT in CFC13), which are derived from partial and non equivalent averaging between the three C2h conformers (see Fig.…”