GAS-PHASE THERMOLYSIS OF PYRAZOLINES .5. ELECTRONIC-STRUCTURE AND GAS-PHASE THERMOLYSIS OF TETRAZOLE DERIVATIVES STUDIED BY PHOTOELECTRON-SPECTROSCOPY

The photoelectron spectra of substituted tetrazoles 1-3, 1,4-dihydro-5 H-tetrazol-5-ones 4-9, and 1,4-dihydro-5H-tetrazole-5-thiones 10-15 ha ve been recorded. Based on PM3 and some ab initio calculations, the io nization potentials have been assigned to molecular orbitals. Gas-phas e thermolyses of 1-15 have been studied by real-time gas analysis cont rolled by photoelectron spectroscopy. Compounds 1 and 2 lose formaldeh yde and thioformaldehyde, respectively, leaving unsubstituted tetrazol e (16), which decomposes mainly through extrusion of a nitrogen molecu le and formation of cyanamide. Thiirane is split off from 3, and the r emaining molecule decomposes into smaller products. Compounds 4-9 are cleaved by [3+2] cycloreversion to isocyanates and azides. Some of the unsymmetrically substituted compounds exhibit a marked selectivity in this reaction. For thiones 10-15 [3+2] cycloreversion is the main way of decomposition affording isothiocyanates and azides. In addition, t he sulfur atom can split off and dimerize or abstract hydrogen atoms t o form hydrogen sulfide. Some products like thiirene, formaldehyde, th ioformaldehyde and acetaldehyde are generated solely from substituents . Photoelectron spectroscopy proved to be an excellent method for such thermolysis studies.