1.2.4.5- Tetrazines special

Another type of special diene, the polyaza benzene heterocyclics, such as triazines and tetrazines, is discussed in Section 6.6.2. 

C3H3N3 and also the tetrazines C2H2N4 are very stable compounds, pentazine CHN5 and hexazine N6, a polymer of nitrogen, do not exist. This is not due to the instability of these molecules as such but to the very special stability of the triple bond in nitrogen and in HCN, compared with the corresponding single and double bonds, while this holds to a much smaller extent for the triple carbon-carbon bond (Table 18). 

Dihydropyridazines are obtained from 1,4-dicarbonyl compounds and hydrazine (Section III,B) or from the reaction of sym-tetrazines and simple ethylenic compounds (Section III,H). There are also a few special reactions, such as that between a tetrahydrofuran and phenylhydrazine, or from a 1,4,5,6-tetrahydropyridazine derivative. The 1,4-dihydro structure has been found to be correct, rather than the 1,6-dihydro structure, postulated earlier for some of these reduced pyridazines (Section III,H). 1,4-Dihydropyridazines can be reduced or oxidized easily and acid treatment of l-tosyl-1,4-dihydropyridazine causes rearrangement to 1-tosylaminopyrrole. ... 

A few years ago, a powerful version of molecular optical spectroscopy with supersonic beams and jets was developed by Smalley, Wharton and Levy . Supersonic expansion of molecules in an inert carrier gas yields an ideal spectroscopic sample. As a result of the expansion, the translational temperature of the carrier gas decreases to extremely low values (below O.I K). The flow is collisionless so that even extremely unstable species survive. Special attention was paid to fluorescence excitation spectroscopy but the technique is by no means limited to this type of spectroscopy. (Because of fundamental difficulties, however, direct measurement of light absorption in molecular beams is not easy.) Cooled molecules in the beam are electronically excited with a tunable dye laser. The emitted fluorescence is detected and plotted against the wavenumber of the exciting radiation. The obtained fluorescence excitation spectrum is generally very similar to the corresponding absorption spectrum. The technique was used for analysis of the spectra of interesting vdW molecules He. .. NOj, He... Ij, X. .. tetrazine and Xj. .. tetrazine (X = He, Ar, H ) complexes . 

All types of spectra of 1,2,4,5-tetrazines have found wide interest. In particular, the electronic spectra of 1,2,4,5-tetrazines have been studied and all bands were assigned to special energy levels only the most important bands will be discussed, for complete information the original literature should be consulted. 

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