Doubly enriched (C-13, N-15) 1-phenyl-3-(alpha-cyano)benzylidenetriazene, Ph-N*=N-N=C(C*equivalent to N)-Ph, did not show C-13-N-15 splittings in the NMR spectra in solution that would be expected from the presence of a cyclic nitrene in reversible equilibrium, a theory proposed in 1964 by Smith, Krbechek, and Resemann to explain its chemical behavior. Molecular orbital calculations at the 6-31G* level on the core structures (Ph replaced by H) also indicated substantially greater stability for the open-chain compound. Flash photolysis (337 nm) of 1,4-diphenyl-5-azido- 1,2,3-triazole in solution led to the open-chain triazene within about 20 ns but with no observable transient absorbing species.