PHOTOELECTRON SPECTROSCOPIC AND COMPUTATIONAL STUDY OF THE THERMOLYSIS OF 1,2,3,6-TETRAHYDRO-1,2,4,5-TETRAZINES

Gas phase thermolyses of 3,6-dimethyl, -diethyl and -di-n-propyl subst ituted 1,2,3,6-tetrahydro-1,2,4,5-tetrazines 1a-1c yielded the corresp onding N-unsubstituted imines 2a-2c. The He(I) photoelectron spectra o f propanimine (2b) and butanimine (2c) are presented for the first tim e. First ionization potentials and orbital energies of the imines as d etermined with B3LYP/6-31 + G//HF/6-31 + G* reproduce the experimenta l data. Ionization bands arising from N,N'-unsubstituted diazetidines 3a-3c could not be detected in the pyrolysis spectra of la-lc. Calcula tions for the extrusion of nitrogen from tetrahydrotetrazine la result ed in a transition state for a [2 + 2 + 2]-cycloreversion that leads t o the imine 2a as product. (C) 1998 Elsevier Science B.V. All rights r eserved.