The electrooptical parameters of aniline and its halogeno derivatives in hydrogen bonded complexes

Abstract

The spectral characteristics of the ν s(NH 2) and ν as(NH 2) IR absorption bands of hydrogen-bonded and free molecules of aniline monobromosubstituted anilines and pentafluoroaniline in CCl 4 have been determined. Dimethylformamide, dimethylsulphoxide and [(CH 3) 2N] 3PO were used as proton acceptors. The analysis of the absorption spectra has been performed in the range 3100–3600 cm −1. The existence of intramolecular hydrogen bonds in o-halogen substituted anilines has been demonstrated. A new method of the determination of the integrated intensity of the stretching vibration band is proposed for free and hydrogen-bonded NH 2 groups in 1:1 complexes when a substantial overlapping of the bands takes place. In the framework of the simplified R-NH 2 model, the normal vibration frequencies ν s(NH 2) and ν as(NH 2) were determined as a function of the force constant K(N-H) and the γ(H-N-H) angle. The ∂μ/∂ q and ∂μ/∂ q′ values of the free and hydrogen-bonded molecules of aniline and its halogen derivatives has been calculated. It was demonstrated that the position of bromine substitution in aniline remarkably effects the electrooptical parameters of free monosubstituted bromoanilines. In hydrogen-bonded complexes this effect is much less pronounced with respect to that of the hydrogen-bonded formation itself. In pentafluoroaniline, the halogen substituent markedly effects the electrooptical parameters for both the free and bonded molecules.