¹³C, ¹H spin–spin coupling. X—Norbornane: A reinvestigation of the karplus curve for ³<i>J</i>(¹³C, ¹H)

Abstract

Abstract 13 C, 2 H spin–spin coupling constants over one, two and three bonds were measured from the 100‐MHz 13 C NMR spectra of deuteriated isotopomers of norbornane‐ d 1 , (1) and fenchane‐2‐ d 1 (2) and also of a number of mono‐deuteriated alkyl‐substituted adamantanes. The magnitudes of the corresponding J ( 13 C, 1 H) values derived from these data by application of the well known relationship J (X, 1 H) = 6.5144 J (X, 2 H) are discussed with respect to the structural data for the hydrocarbons, which were taken from force field calculations with the Allinger MM2 method. In particular, the dihedral angle dependence and the Karplus curve for 3 J ( 13 C, 1 H) are investigated. Coupling constants calculated by the FP‐INDO method are compared with the experimental data, and the effect of substitution by additional CC bonds in α‐, β‐ and γ‐positions of the 13 C‐αC‐βC‐γH bond fragment is elucidated. If substituent effects that arise through branching and methyl substitution in 1 and 2 are taken into account for dihedral angles ϕ &gt; 90°, one derives 3 J ( 13 C, 1 H) = 4.50 − 0.87 cos ϕ + 4.03 cos 2ϕ with J (0°) = 7.7, J (60°;) = 2.0 and J (180°) = 9.4 Hz.