Theoretical study of the hex-3-ene radical cation

Abstract

The ground-state equilibrium geometries of seven different conformational structures of the hex-3-ene radical cation have been investigated, using ab initio unrestricted Hartree–Fock (UHF) and second-order Møller–Plesset perturbation (MP2) calculations, in conjunction with the 6-31G** and 3-21G basis sets, respectively.

Configuration interaction calculations, including single and double excitations (SDCI), have subsequently been performed on the optimized geometries in order to obtain accurate spin properties.

The isotropic hyperfine coupling constants (hcc) for the hydrogen atoms are reported and compared with experimental data. The unpaired electron is found to be located mainly in the central but-2-ene-like part of the molecule, with the hyperfine structure essentially being determined by the local geometry around the double bond. The relative orientation of the terminal CH₃ groups are, on the other hand, found to be relatively unimportant for the hcc values. The results are compatible with a planar arrangement around the double bond in the E isomer, but indicate a twist around this bond in the Z isomer.