ELECTRONIC ABSORPTION-SPECTRA OF SOME NICOTINAMIDES AND NICOTINIC ACIDS - MOLECULAR-ORBITAL TREATMENT

The electronic absorption spectra of the position isomers nicotinamide and isonicotinamide, nicotinic acid, and isonicotinic acid were inves tigated, together with the spectra of thionicotinamide, N-methyl nicot inamide and nicotinic acid N oxide. Apparent differences in the spectr a of the position isomers were interpreted in terms of the torsion ang le between the planes of the molecule, the height of the barrier to in ternal rotation, and the results of molecular orbital (MO) calculation s. The largest perturbation effect was observed in the case of thionic otinamide whereas the smallest effect was observed in the case of nico tinic acid N oxide. MO calculations have indicated the existence of ov erlapping transitions. The observed transitions proved to be pi-pi tr ansitions, none of the n-pi was observed. (C) 1997 John Wiley & Sons, Inc.