Anomeric effects in fluoro and trifluoromethyl piperidines: a computational study of conformational preferences and hydration

摘要: A computational investigation of anomeric effects in piperidine rings bearing fluoro and trifluoromethyl substituents shows for both compounds the most pronounced evidence effect, as expressed hyperconjugative delocalization nitrogen lone pair, structures with substituent axial position N–H bond equatorial position. This structure is lowest-energy case but not where there an increased penalty associated CF3 group. The effect characterized via geometrical evidence, natural orbital analysis, electrostatic effects, energetic criteria. Computational results from a variety levels theory are presented including CCSD(T) complete basis set extrapolation, B2PLYP-D, ωB97XD, B97-D, M06-2X, B3LYP, MP2 allowing comparison performance. CCSD(T)/CBS very well represented by either B2PLYP-D or ωB97XD moderate to large sets (aug-cc-pVTZ aug-cc-pVDZ). Hyperconjugation, steric play role relative ordering isomers considered.