Parity and heteroatom effects on open-shell exchange interactions: nitrenophenyl iminoylnitroxides.

Photolysis of pN3PhIN and mN3PhIN in frozen matrix yields pNPhIN and mNPhIN, respectively. pNPhIN gives a quartet state with nonlinear ESR intensity behavior (|D/hc| = 0.300 cm(-1), |E/hc| congruent with 0.

Photolysis and oxidation of azidophenyl-substituted radicals: delocalization in heteroatom-based radicals.

2-(4-Azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (14), 2-(4-azidophenyl)benzimidazole-1-oxide-3-oxyl (16), 2-(4-azidophenyl)-1,2,6-triphenylverdazyl (19), 2-(3-azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (21), and (3-azidophenyl)-N-tert-butyl-N-aminoxyl (25) were photolyzed in frozen solution to give S = 3/2 state ESR spectra of the corresponding nitrenophenyl radicals with the following zero-field splitting parameters: |D/hc| = 0.277 cm(-1), |E/hc| < or = 0.002 cm(-1) (7 from 14); |D/hc| = 0.

Molecular recognition for stable organic radicals--2-(6-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl.

Stable radical 2-(6-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl shows antiferromagnetic spin pairing with 2J/k= -14 K, attributable to a close contact between unpaired spin density on the imidazole-type nitrogen atoms; hydrogen bonds aid dimer formation, but do not appear to play an eletronic role in the magnetic behaviour.

Limits of delocalization in through-conjugated dinitrenes: aromatization or bond formation?

[reaction: see text] Dinitrenes 4 and 5 both can form quinonoidal structures by conjugative bond formation. However, ESR spectroscopy detects a thermally populated, excited-state, triplet quinonoidal structure only for 4, with a zero-field splitting of |D/hc| = 0.0822 cm(-)(1), |E/hc| congruent with 0.