Computational study of stereoelectronic effects in fluorinated alkylamines

Abstract

AbstractA systematic evaluation of the stereoelectronic effects in a series of fluorinated amine compounds has been carried out. A variety of computational methods have been employed, including molecular mechanics, semi‐empirical, density functional and ab initio methods. An analysis of the natural bond orbital populations has been carried out and the effect of solvent was considered via the polarized continuum model (PCM). The results indicate a preference for conformations that result in an anti‐periplanar arrangement between the nitrogen lone pair and the CX bond (XF or CF3). There are variations in geometry and natural bond orbital population, with conformation that are consistent with a stereoelectronic effect whereby electron density from the nitrogen lone pair is delocalized into the CX σ* orbital. Similar results are obtained for trifluoromethyl methylamines, although the magnitude of the stereoelectronic effect is attenuated resulting in greater expected conformational diversity for these compounds. The PCM results suggest that these preferences should persist in solution. Comparison among the computational methods used reveals that there is good agreement among the ab initio and density functional methods (at the HF/6‐31 + G(d), MP2/6‐31 + G(d), MP2/6‐311 + G(2d,p) and B3LYP/6‐31 + G(d) levels) and these methods agree well with the available experimental data for ethylmethylamine. Published in 2005 by John Wiley & Sons, Ltd.