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Abstract

The solid and solution IR spectra of the yellow formazans (1) show in most cases a strong J'(NH) or ν (ND) band. The ν (NH) absorption of the red formazans (2) is so weak (ε ≈ 1 [liter mole-1 cm-1]), that it is only observed in solutions and with long path length. In the case of C-ethoxycarbonyl-N.N′-diphenylformazan opening of the intramolecular N — H - - - N hydrogen bridge by light gives rise to a new intramolecular N — H - - - O hydrogen bridge. The nuclear N — H resonance of the red formazans is shifted far to low field (14 p. p.m.).