BONDING IN PHENYLHYDRAZONES - X-RAY CRYSTAL-STRUCTURE AND THEORETICAL CALCULATIONS INVOLVING (E)-ACETOPHENONE PHENYLHYDRAZONE

Semiempirical (PM3 type) calculations have been carried out on the E isomer of acetophenone phenylhydrazone and extended to include acetophenoneimine and phenylhydrazone. The optimized structure of acetophenone phenylhydrazone has also been compared with the solid state structure obtained from the results of an X-ray crystal structure determination. The crystals are monoclinic, space group P2(1)/c, a = 5.520(2)angstrom, b = 8.944(3)angstrom, c = 23.591(8)angstrom, beta = 90.28(3)-degrees, and V = 1164.7(7)angstrom3. The final R value is 0.0549 for 1097 reflections with F > 3sigma(F). The structure possesses a planar conformation and both N atoms possess trigonal-planar geometries. Results of the theoretical calculation are in good agreement with those obtained from the crystallographic data and indicate that conjugation between the hydrazone region and the phenyl rings plays a significant role in favoring a planar molecular conformation and has a significant perturbing influence on the bond lengths and angles associated with the hydrazone C=N-N atoms. A Mulliken analysis for the structure gives bond orders of 1.77 and 1.10 for the formally double bonded C-N and single-bonded N-N atoms, respectively.