Molecular Orbital Calculations on the Electronic Structures of Some Arylhydrazones

The geometry and electronic structure of the parent formaldehyde hydrazone and some ethylcyanoacetate phenylhydrazones (ECPHs) are studied at the semiempirical level of MO theory using the AM1 method. The effect of substitution on the geometry of the hydrazone moiety is investigated. The optimized geometry of formaldehyde hydrazone is nonplanar while in the ECPHs the planarity of the hydrazone group and its coplanarity with the phenyl ring increase in the direction of the electron-attracting ability of the para substituent. This has been attributed to an increase in the p-π conjugation between the lone pair of electrons on the amine nitrogen and the phenyl ring. Variations of ionization potentials and bond orders with the Hammett constant, σ_p, are examined and straight-line relationships are obtained. The results are correlated with the observed variations in the experimentally measured electrical conductivities of the studied compounds.