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Gas‐Phase Thermolysis of Pyrazolines, 2 [1] . Electronic Structure and Gas‐Phase Thermolysis of 4,5‐Dihydro‐3 H ‐pyrazoles Studied by Photoelectron Spectroscopy, Semiempirical Quantum‐Chemical Calculations, and Flash Vacuum Pyrolysis
Author(s) -
Kindermann Markus Karl,
Kowski Klaus,
Muchall Heidi M.,
Rademacher Paul
Publication year - 1993
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19931261217
Subject(s) - chemistry , mndo , thermal decomposition , ionization energy , molecule , pyrolysis , molecular orbital , x ray photoelectron spectroscopy , thermal stability , gas phase , photoemission spectroscopy , decomposition , computational chemistry , ionization , organic chemistry , nuclear magnetic resonance , ion , physics
The PE spectra of the 4,5‐dihydro‐3 H ‐pyrazoles 1, 2 , of 2,5‐dihydro‐1,3,4‐oxadiazole 3 , and 2,5‐dihydro‐1,3,4‐thiadiazole 4 have been recorded. Based on HAM/3, MNDO, AM1, and PM3 calculations, the ionization potentials have been assigned to molecular orbitals. The gas‐phase thermolyses of 1–4 have been studied by PE‐controlled gas analysis. Extrusion of molecular nitrogen leads to reactive species which cyclize to three‐membered rings of different stability. At higher temperatures and in flash vacuum pyrolysis, consecutive reactions may lead to smaller acyclic molecules. The cyclo‐propanol 7 , obtained by denitrogenation of 2 , is thermally rather stable. Its PE spectrum has been recorded and analyzed.