Molecular orbital theory in mass spectrometry: ab initio calculations on 2-methylpropene and the 2-methylpropene radical-cation

Abstract

Electronic structures have been calculated ab initio by the self consistent field molecular orbital method for 2-methylpropene and two states of the 2-methylpropene radical-cation. The energy difference between the 2 B 1 planar and 2 B 2 perpendicular states of the radical-cation is about 67 kJ mol -1 . The participation of the 2 B 2 state in a proposed 1, 3-hydrogen shift lifts the orbital symmetry restriction predicted for this process in the case of the 2 B 1 state. Because more than one state of a radical-cation may be populated, calculation of the electronic structures of the low-lying states of the ion is a prerequisite for secure application of orbital symmetry rules in mass spectrometry.