Theoretical study of Jahn–Teller distortions in C6H+6 and C6F+6

Abstract

Ab initio molecular orbital theory with the 6–31G basis set is used to study Jahn–Teller distortion effects in the benzene cation (C6H+6) and the perfluorobenzene cation (C6F+6). π-electron correlation is included in these calculations. Completely optimized Jahn–Teller distorted geometries are obtained for the ground electronic states of both C6H+6 and C6F+6. The stabilization energies resulting from these distortions are calculated for both systems. The stabilization is partitioned into contributions from C–C stretch, C–H or C–F stretch, C–C–C bend, and C–C–H or C–C–F bend coordinates. Detailed comparison is made between C6H+6 and C6F+6 to consider the effects of substitution. The calculated geometries and stabilization energies for C6F+6 are compared to values derived from laser-induced fluorescence experiments. The overall calculated distortion parameters for C6F+6 are in good agreement with the experimentally derived distortions, though the calculated C–C bond length change is somewhat larger than the experimentally derived value. The total calculated stabilization energy (≂1000 cm−1) is in good agreement with the experimental value (820±≂100 cm−1). The individual stabilization energy contribution for the C–C stretch mode is calculated to be larger than the experimental estimate, paralleling the overestimation of the C–C bond length change for this mode. The other stabilization parameters are in reasonably good agreement with the experimental values.