Theoretical calculations and experimental studies on the electronic structures of hydrazones and hydrazone radical cations: Formaldehyde hydrazone and benzaldehyde diphenylhydrazones

Abstract

The geometry and electronic structure of the parent formaldehyde hydrazone, benzaldehyde diphenylhydrazone (BDPH), and p-(diethylamino)benzaldehyde diphenylhydrazone (DEH) are studied by using ab initio SCF calculations, electrochemical measurements, and electronic absorption spectroscopy. The computer-optimized geometries for formaldehyde hydrazone indicate that the neutral species is nonplanar while the radical cation is planar. The optimized geometry for BDPH and the experimental geometry for DEH reveal that the structure of the hydrazone group in the neutral systems is planar, or very close to planarity; this change is attributed to an increase in p-π conjugation between the lone pair of electrons on the hydrazone amine nitrogen and phenyl rings. The best representation for the structure of the radical cations of formaldehyde hydrazone and BDPH is one with the unpaired electron residing on the hydrazone amine nitrogen; however, the best description for the structure of the radical cation of DEH is one with the unpaired electron not on the hydrazone amine but on the aniline nitrogen. © 1990 American Chemical Society.