Stereoelectronic effects: Perlin effects in cyclohexane-derived compounds

Abstract

Stereoelectronic effects in cyclohexanones, methylenecyclohexanes, spiro, and epoxy compounds of cyclohexanes and further derivatives were investigated by measuring 1JC,H coupling constants and by identification of Perlin effects, that is, of differences in the coupling constants for equatorial and axial CH bonds in the methylene groups of six-membered rings. The Perlin effects were correlated with results from natural bond orbital analyses. NMR experiments and calculations were performed with conformationally restricted 4-tert-butyl-substituted derivatives. It turned out that the coupling constants are strongly influenced not only by stereoelectronic interactions with CC, CO, and CN p bonds, or with the p-type CC or CO bonds of the three-membered rings, but also by the s character of the respective CH bonds' carbon orbital. Reliable correlations of measured and calculated coupling constants were achieved with B3LYP/6-311++G(d,p) and BP86/aug-cc-pVTZ-J functionals.