Carbon—Carbon Spin-Coupling Constants in Characteristic CC-Bond Types

Abstract

Carbon—carbon spin-coupling constants have been measured for a variety of types of CC bonds (in C13-enriched compounds), usually characterized by the different hybridizations of the C atoms. For hydrocarbons in which these bond types appear, the CC spin-coupling constant is proportional to the product of the s characters of the carbon atoms forming the bond in question. For several substituted hydrocarbons ``modified s characters'' may be found, from which the spin-coupling constants can be calculated by means of the same proportionality factor found for the hydrocarbons. The enhancement in CC spin-coupling constant due to pi electrons seems pronounced for double and triple bonds but less so in acyclic conjugated systems. A simple correlation of CC-bond distance and CC-coupling constant does not exist in general, but has been found for CC single bonds in hydrocarbons.