Crystallographic evidence for the electronic distribution in (2,4-cyclopentadien-1-ylidenehydrazono)triphenylphosphorane

The title compound, C23H19N2P, can be graphically represented by several ca nonical forms. Its crystal structure analysis shows a clear bond alternatio n in the cyclopentadiene ring, which continues in the azo substructure, ind icating that the resonance form containing the nonaromatic neutral cyclopen tadienylidene moiety describes the actual hybrid form better than other 'in ner ionic' resonance forms containing the aromatic anionic cyclo-pentadieny lic portion. The preference for an s-transoid (E) geometry for the P1-N1-N2 -C1 substructure was also confirmed over the other possible s-cisoid (Z) co nformer.