The electronic structures of non-Kekulé-type isoelectronic molecules 1,3,5-trimethylenebenzene (TMB) and 1,3,5-triaminobenzene trication (TAB 3+) having a threefold axis are discussed with the ab initia molecular orbital (MO) method. The quartet state with a D3h geometry is predicted to be the ground state of TMB and TAB3+. According to the Jahn-Teller theorem, the doublet 2E″ states of TMB and TAB3+ are subject to the first order distortions which remove the degeneracy. The quartet-doublet energy splittings are calculated for these non-Kekulé-type molecules at the second order Møller-Plesset (MP2) perturbation level of theory. In TMB the 4A″2 state with a planar D3h geometry is predicted to lie well below the 2A2 state with a planar C2υ geometry in which one of the methylene groups has a longer C-C bridge bond connecting with the benzene ring. Moreover, in TAB3+ the 4A″ 2 state with a planar D3h geometry also lies well below the 2A2 state. The 2A2- 2B1 energy splittings on the pseudorotation potential surface overestimated at the unrestricted Hartree-Fock (UHF) level are corrected with the MP2 method.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry