C13-H Coupling in Hydrocarbon Molecules

The electron coupled nuclear spin-spin interaction between a C 13 and a proton in a chemical bond in hydrocarbon molecules is investigated theoretically. The lower limit of an electronic correlation effect on the coupling constant is estimated semi-empirically. The result shows that the coupling constant is inversely proportional to the valence number of the C 13 atom, and is almost unaffected by a substitution at the end of the molecule, if the symmetry of the molecule is not altered by the substitution.