Carbon-13-proton coupling constants in cyclohexane

Abstract

Recently much interest has been shown in the study of 13C-'H coupling constants.1 The data on 13C-'H couplings in flexible saturated systems are, however, rather limited, owing to extreme complexity of their proton-coupled 13C NMR spectra.We wish to report here the experimental values of all possible 13C-]H coupling constants in cyclohexane which is a classical example of a conformationally flexible system. The data discussed below were obtained from the lowand hightemperature proton-coupled 13C spectra of cyclohexane-

Conformational analysis of a 12‐membered crown dithioether in the solid state and in solution

“…10,11 We performed a partial analysis of proton-coupled 13 C NMR spectrum for solution of 1 in C 6 D 6 , which provided us with experimental values of vicinal couplings of the methyl carbon atom 3 J C(13)H(9c) and 3 J C(13)H(9t) ( Table 7 and Table 8). These parameters were also calculated for all 28 individual conformers using the Karplus equation 11 , and then we estimated C-H coupling for the A, B and C macroconformers by averaging with the Boltzmann weight factor within each group.…”

Variation in protein Cα‐related one‐bond J couplings

“…[28,29] Conformational dependence of 1 J CH and 1 J CC couplings on circumjacent torsion geometry is inferred from a difference in coupling constants observed for axial and equatorial substituents in cyclohexanes. [30,31] Both 1 J CH and 1 J CC couplings are of utility to conformational analysis of carbohydrates. [32,33] The measurement of 1 J CαHα in conformationally constrained cyclic oligopeptides revealed a dependence of the coupling magnitude on the polypeptide main-chain torsion angles φ and ψ.…”

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 8—Monocycloalkanes

“…All calculations are performed within the C 1 symmetry point group (no symmetry constraints applied Following the known structural trends of carbon-hydrogen couplings, 94,95 both geminal and vicinal couplings were assigned as negative and positive, respectively, whereas both four-bond couplings were assumed to be negative. 93 All 21 spin-spin couplings of chair cyclohexane, namely three J(C,C), eight J(C,H) and 10 J(H,H), calculated at the SOPPA and SOPPA(CCSD) levels and compared with available experiment, are presented in Tables 1-3 together with the corresponding RPA results. The latter were included only for the purpose of estimating the effects of electronic correlation (see next section).…”

“…It is noteworthy that our present SOPPA and SOPPA(CCSD) calculations unambiguously confirmed the signs of 2 J C,C , 4 J C,H a and 4 J C,H e , which were assumed to be negative in the original experimental studies. 91,93 Recently, Bagno et al 96 performed DFT calculations of the eight possible J(C,H) in the frozen cyclohexane taking into account only three terms (Fermi contact, diamagnetic and paramagnetic spin-orbit contributions). Geminal, vicinal and four-bond couplings were well reproduced by those calculations whereas one-bond J(C,H) were considerably underestimated (by ca 9-13 Hz) owing to the too small Fermi contact contributions.…”