Ab initio and experimental studies on structure and vibrational spectra of some partially reduced benzo[c]phenanthrenes

A systematic study has been conducted on the conformation, electronic structure and vibrational spectra of benzo[c]phenanthrene and some of its partially reduced derivatives by experimental infrared spectroscopic and quantum chemical techniques. Electrostatic potential surfaces have been mapped over the electron density isosurfaces to obtain information about the size, shape, charge density distribution and chemical reactivity of the molecules. Possibility of hydrogen-hydrogen bonding has been explored in all the molecules. Partial reduction of the aromatic rings in benzo[c]phenanthrene leads to considerable molecular distortion with the approximate mean angle between the terminal rings increasing from 27.3° to 46.0°. The distortion is unequally distributed near the aromatic and saturated rings; the latter absorbs most of strain due to flexibility of the rings. A complete vibrational analysis of the experimental infrared spectra has been reported on the basis of frequency and intensity of the vibrational bands and potential energy distribution over the internal coordinates and characteristic bands have been identified.