The DNP-derivatives of diphenylcyclopropenone 4-azatriafulvenes

The reaction of diphenylcyclopropenone and 2,4-dinitrophenylhydrazine in the presence of an acid gives directly either the 2,4-dinitrophenylhydrazone (II) or its salts (VII), The products are interconvertible. The ease of formation of VII from the 4-azatriafulvene derivative II by addition of a proton is explained by the significantly higher contributions, in the ground state, of dipolar structures such as VIIa as compared to IIa. The 4-azatriafulvene cation is characterized by a sharp IR absorption at 1900 cm^-1.