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|≌ 0.0 cm-1. The tendency to maintain aromaticity in the additional ring of 5 favors a dinitrene structure (with one less formal π-bond) over a quinonoidal structure. The thermally populated quintet ...
