Semi-empirical MNDO SCF-MO study of ion radicals derived from tricyclo[3.3.3.0]undecane, and from some related alkanes

Abstract

Molecular geometries have been calculated, using the MNDO method, for the cation and anion radicals derived from tricyclo[3.3.3.0]undecane ([3.3.3]propellane), for the corresponding neutral alkane and its dication, and for the cation radicals derived from the related series of acyclic alkanes: Me₃CH, Me₃CMe, and Me₃CCMe₃. Hyperfine coupling constants have also been calculated for these radicals. The two radicals derived from [3.3.3]propellane have very similar molecular and electronic structures, and differ principally in the character of the unique C–C bond, a one-electron σ bond in the cation and a three-electron σ* bond in the anion. Both the cations Me₃CMe⁺ and Me₃CCMe₃⁺ are calculated to be unstable as isolated species to dissociation into Me₃C⁺ and CH₃˙ or Me₃C˙ respectively, a conclusion supported by experimental gas-phase data; the observed hyperfine couplings allow deductions to be made about their structures in frozen solution. Two isomeric structures have been calculated for the cation Me₃CH⁺, having calculated proton hyperfine couplings in reasonable agreement with those observed experimentally.