H-Diazirine

Brunner et al. (1980) have reported on the properties of a new class of aryl diazirines, the 3-aryl-3-trifluoromethyldiazirines. Besides forming a class of the most attractive photoactivatable reagents available, these molecules may be made in far higher yield than the corresponding 3-H-diazirines. The route used, which incidentally fails with the 3-H-com-pounds (Smith and Knowles, 1975), is shown in Fig. 3.24. Two drawbacks are the large number of steps involved and the difficulty of preparing... 

We have examined both isomeric diazirines, 3 H-diazirine with an N=N bond and 1 H-diazirine with a C—N bond. 3 H-diazirine is known and its structure has been determined by microwave spectroscopy. 4) In the STO-3G determination we have assumed Czv symmetry, leading to the structure compared with experiment in Fig. 1. The N=N bondlength is... 

The most stable isomer of CN2H2 is predicted to be cyanamide, NH2—C=N, according to the 6-31G basis. ) 3 H-diazirine is predicted to be 50.0 kcal/mol less stable. There have been a number of previous ab initio molecular orbital calculations on 3 H-diazirine. - - ) These are listed in Table 11 together with calculated energies and dipole moments. 

The 4-3IG calculations show that the trans isomer is more stable than the cis by 7.7 kcal/mol. However, both are much less stable than 3 H-diazirine (by 41.9 kcal/mol for fraws-diaziridinylidene). 

The cyclic form of CN 2 can be obtained formally by abstraction of two methylene hydrogens in 3 H-diazirine. This gives a singlet carbene structure symmetrically connected to an N—N bond and an aromatic system with two sr-electrons. However, the energy is substantially higher (by 48.7 kcal/mol with 4-31G) than the lowest singlet of the open form NCN (cyanonitrene) which is linear with Doo symmetry, si)... 

This molecule is the third member of the isoelectronic series 3 H-diazirine (18), triazirine (28) and oxadiazirine (30). Its structmre was determined... 

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