Stereochemical Dependence of ³J_CH Coupling Constants in 2-Substituted 4-t-Butyl-cyclohexanone and Their Alcohol Derivatives

Abstract

Theoretical and experimental studies on (3)J(C2H6eq) NMR spin-spin coupling constants in both the 2-X-4-t-butyl-cyclohexanone (X = H, CH(3), F, Cl, and Br) and in their alcohol derivatives series are reported. Results thus found are rationalized in terms of the transmission of the Fermi contact contribution to such couplings. To this end, dependencies of (3)J(C2H6eq) couplings versus the C(2)-C(1)-C(6) angle are compared in both series for equatorial and axial X orientations. The main trend is described in terms of the rear lobes interaction. Besides, for X = halogen atom in equatorial orientation a rather strong interaction between oxygen and halogen lone pairs is observed, and its influence on (3)J(C2H6eq) couplings is discussed and rationalized in terms of different Fermi contact transmission pathways.

Unexpected Geometrical Effects on Paramagnetic Spin–Orbit and Spin–Dipolar 2JFF Couplings

“…In the particular case of 2 J FF SSCCs in fragments of type F–C–F very important contributions originating in the PSO and SD terms are known, and they are surprisingly sensitive to electron-withdrawing groups bonded to the intermediate C atom. , To understand factors determining such unusual trends, in this study we applied a semiqualitative approach, reported previously, specially suited to understand electronic factors originating trends of high-resolution NMR parameters. As shown below, when applying this model, it is predicted that the isotropic value of either the PSO or the SD terms may depend rather strongly on the angles formed by each C–F bond containing the coupling nuclei and the eigenvectors of the respective tensors.…”