Structure of the cyclohexa-1,4-diene radical cation: an ab initio molecular orbital and electron paramagnetic resonance study

Abstract

The structure of the radical cation of cyclohexa-1,4-diene, (1⁺), was explored using ab initio MO calculations and EPR spectroscopy. Geometry optimizations were carried out on neutral 1 and 1⁺ at the (U)HF/6-31G(d, p) and MP2/6-31G(d, p) levels of theory. The ground states of both 1 and 1⁺ were found to possess D_2h structures, in agreement with experimental data. The ground electronic state of 1⁺ was found to be ²B_1u and not ²B_3g, and this is the result of through-bond orbital interactions. The computed MP2/6-31G(d, p) proton isotropic hfs values for 1⁺ were found to be in good agreement with the experimental values. The EPR spectra and proton hfs values for 1⁺ are similar to those obtained earlier by Shida et al.