The geminal inter-proton coupling constants J(H-C-H) were obtained from the N.M.R. spectra of suitably deuterated compounds MenX where X = C, Ge, Sn, Pb, 0, S, I, N, and Li. The relation between the magnitudes of J(H-C-H), J(13C-H), and electronegativity of X in this series is explored and some correlations are proposed. The data for methyllithium do not fit with the remainder of the results. It is tentatively concluded that in this series of compounds J(H-C-H) is a periodic property.