Nitrenes zero-field parameters

Zero-Field Parameters of Some Intermediate Ground-State Triplet Nitrenes Produced by Photolysis3... 

Table 3. Zero field splitting parameters for nitrenes...

The smaller the value of D, the smaller the interaction between the unpaired electrons, or in other words the greater is their separation. So, from the zero field splitting parameter of phenylnitrene (D =0.99 cm-1) one can deduce that one unpaired electron is delocalized into the aromatic system. Although ESR shows that these nitrenes have triplet ground states it tells nothing about the electronic state of the nitrenes at the moment of generation. 

The stability to the photochemieal rearrangements with the triazine eyele expansion in the triplet nitreno-l,3,5-triazines inereased with an inerease in the D-parameter of splitting in zero field found from the ESR spectra, which, in its turn, correlated with the spin density on the nitrene center calculated quantum-chemically [87], Triplet nitrenes with D/hc > 1.40 cm and pa > 1.77 (UB3LYP/6-31G ) were photochemically very stable and did not rearrange into carbodiimides. 

The stabilizing effect of the chlorine atoms manifested itself also in the photolysis of 2,4,6-triazido-3,5-dichloropyridine TAP (methyltetrahydrofuran, 77 K), when one managed to successively observe and characterize mono-, di-, and trinitrene (dicyano derivative failed to produce high-spin nitrenes) [89, 95, 96]. It was found that, with an increase in the multiplicity (the number of the nitrene centers), the absorption spectrum shifts bathochromically, and the /)-parameter of splitting in zero field decreases (Table 17). 

S.V. Chapyshev, Zero-field splitting parameters of triplet nitreno-s-triazines a new insight into the geometry of the nitrene centres of triplet and singlet mtisaes, Mendeleev Commun., 2002,12,227-229. 

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