DFT calculations and NMR measurements applied to the conformational analysis of cis and trans-3-phenylaminocyclohexyl N,N-dimethylcarbamates

Abstract

The three-dimensional structure of a potential drug molecule is of critical importance. Factors that determine its conformational stability and, consequently, corresponding biological/physicochemical properties of interest must therefore be carefully analyzed. Conformational properties and molecular structures of cis and trans-3-phenylaminocyclohexyl N,N-dimethylcarbamates were studied by low temperature 1H and 13C NMR spectroscopy and electronic structure calculations. B3LYP and M06-2X methods associated with the 6-311++G(2df,2p) basis set, and the integral-equation-formalism polarizable continuum model were used to study the conformational preferences in dichloromethane, acetone and methanol. NMR measurements indicated that for the cis isomer, the conformer with both substituents in equatorial position is the most stable, while for the trans isomer, the conformer with the carbamate group in the axial position and the arylamine in the equatorial position is favored in all solvents. B3LYP/6-311++G(2df,2p) theory level associated with IEF-PCM described properly the conformational preference in solution. NBO analyses were applied to determine the importance of hyperconjugative interactions in the conformational equilibrium.