194
H. M. Muchall, P. Rademacher / Journal of Molecular Structure 471 (1998) 189–194
Table 3
Total energies ET (au) and selected bond lengths r (pm) of 1a and its transition state TS for symmetrical nitrogen extrusion according to HF/6-31
+ G*
ET
r(N1yN2)a
r(N2–C3)a
r(N4–N5)a
1a
TS
−375.000327
−374.898283
121.2
112.9
147.5
190.1
140.2
175.2
aAtom numbers according to Fig. 2.
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4. Conclusion
The pyrolyses of 1,2,3,6-tetrahydro-1,2,4,5-tetrazines
1a–1c yielded the imines 2a–2c, respectively. While
the presence of ethanimine (2a) was established through
a comparison of its literature PE spectrum with the
obtained pyrolysis spectrum of 1a, this procedure
could not be used for 2b and 2c because their PE spectra
were not known. As B3LYP/6-31 + G*//HF/6-31 + G*
calculated first vertical ionization potential and relative
orbital energies for 2a matched the experimental data
perfectly, similar calculations were performed for
propanimine (2b) as well as butanimine (2c) and corre-
lations with recorded values were found to be excellent.
Diazetidines 3a–3c are not products of the pyrolyses as
was concluded from the computationally predicted first
vertical ionization potential which could not be located
in the thermolyses spectra of tetrazines 1a–1c. A ratio-
nalization for the formation of imines as opposed to
diazetidines in the pyrolyses was possible from a com-
putational study of the thermolysis of 1a. The transition
state for nitrogen extrusion is representative of a [2 + 2 +
2]-cycloreversion.
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Acknowledgements
We thank the Fonds der Chemischen Industrie,
Frankfurt am Main, for financial support.
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