The relationship between proton-proton NMR coupling constants and substituent electronegativities—I : An empirical generalization of the karplus equation

A new coupling constant-torsion angle relation for the three-bond ¹H-¹H spin-spin coupling constant is formulated. The relation includes a correction for the electronegativity of substituents. The correction term is written as a function of the electronegativity, the H-C-C-H torsion angle, and the orientation of each substituent relative to the coupled protons. A dataset consisting of 315 experimental coupling constants was used to derive six empirical parameters by means of an iterative least-squares minimization procedure. The precision of the proposed equation, expressed as the root-mean-square deviation (0.48 Hz), is superior to any hitherto reported. It is shown that separate treatment of CH₂CH₂, CH₂CH and CHCH fragments even improves this precision. An application in the field of monosubstituted cyclohexanes is given.