On the search of cumulative effect of fluoro-substituents in the structural and vibrational properties of sulfinylanilines: Study of 3,4-difluorosulfinylaniline and 2,3,4-trifluorosulfinylaniline

Abstract

The study of substitution effects on the structural and vibrational properties of a series of recently reported mono fluoro-substituted sulfinylanilines proceeds a step forward with the present study of 3,4-difluorosulfinylaniline and 2,3,4-trifluorosulfinylaniline. These substances were synthesized and characterized by FTIR, Raman and NMR spectra, which were subsequently compared with theoretical spectra, obtained by quantum chemical calculations at different levels of theory. The number of signals in the vibrational spectra, together with the analysis of the potential energy surface of both compounds reveal the presence of stable conformers possessing the angular NS→O group in a syn conformation of the CN and S→O bonds and coplanar with the ring plane. According to the Natural Bond Orbital analysis performed, the prevalence of a given structure of the stable syn conformer over other local minima of the potential energy surface obtained upon rotation around the NS and CN bonds is a consequence of different orbital interactions. The planar conformation predicted for stable minima are stabilized by conjugation between the π-systems of the NS→O group and the ring and by a weak orbital interaction between oxygen and the ortho hydrogen closest to it.