Photoelectron spectroscopic and computational study of the thermolysis of 1,2,3,6-tetrahydro-1,2,4,5-tetrazines

Article abstract of DOI:10.1016/S0022-2860(98)00398-6

Gas phase thermolyses of 3,6-dimethyl, -diethyl and -di-n-propyl substituted 1,2,3,6-tetrahydro-1,2,4,5-tetrazines 1a-1c yielded the corresponding N-unsubstituted imines 2a-2c. The He(I) photoelectron spectra of propanimine (2b) and butanimine (2c) are presented for the first time. First ionization potentials and orbital energies of the imines as determined with B3LYP/6-31 + G*//HF/6-31 + G* reproduce the experimental data. Ionization bands arising from N,N'-unsubstituted diazetidines 3a-3c could not be detected in the pyrolysis spectra of 1a-1c. Calculations for the extrusion of nitrogen from tetrahydrotetrazine 1a resulted in a transition state for a [2 + 2 + 2]-cycloreversion that leads to the imine 2a as product.