Nuclear Magnetic Resonance Spectra of ortho-Haloanilines-Analysis of Four-Spin Systems and Study of Solvent Effects

Abstract

The NMR spectra of ortho haloanilines measured in various solvents were analyzed as ABCD spin systems and the proton chemical shifts and spin-spin coupling constants were determined. Upon these data, solvent effects on the internal chemical shifts were investigated. The main feature in the solvent effects was the selective deshielding of the proton ortho to the amino substituent in polar solvents. The above shift in polar solvents was explained by a specific solute-solvent association involving a hydrogen-bonding formation which was competitive with the intramolecular interaction between the substituents and a polar mesomeric structure of the solute molecule was also considered for the explanation of the variation of the other internal chemical shifts. Furthermore, the solvent shifts in inert solvents and toluene were discussed. The proton chemical shifts of the isolated molecules were found to have large departures from those predicted by the additivity rule.