Photolysis (254 nm) of CF 3 N 3 in pentane at 6-10 K produced a persistent electron paramagnetic resonance spectrum typical of a triplet nitrene centered at 8620 G. The spectrum (|D/hc| ) 1.736 cm -1 ) is attributed to triplet CF 3 -N, and is very similar to that of triplet NH (|D/hc| ) 1.863 cm -1 ) and CH 3-N (|D/hc| ) 1.720 cm -1 ) which were reported previously. CF 3 N 3 was also deposited in an argon matrix at 14 K. The azide (λ max ) 257 nm) was decomposed by exposure to 254 nm light with the concurrent formation of sharp, structured absorption bands at 342, 347.5, and 354 nm. The UV bands are assigned to the triplet nitrene CF 3 N on the basis of its similarity to the spectrum of CH 3 N and time-dependent density functional theory (B3LYP) calculations.

On the basis of the open-shell electronic structure of the lowest-singlet state of phenylnitrene, it is predicted that substitution of a radical-stabilizing cyano group at an ortho carbon should facilitate cyclization at that carbon, whereas cyano substitution at the para carbon should retard the rate of cyclization. These qualitative predictions have been tested computationally by performing (8/8)CASSCF and CASPT2/6-31G* ab initio calculations and experimentally by carrying out laser flash photolysis and chemical trapping studies. The calculations and experiments both find that, unlike the case with ortho fluoro and ortho methyl substituents, the rate of cyclization at a substituted carbon is not retarded by an ortho cyano group. In contrast, a para cyano group is found, both computationally and experimentally, to raise the barrier to cyclization of singlet phenylnitrene by >1 kcal/mol.