Ultrahigh resolution in proton NMR spectra at 500 MHz: two-bond intrinsic chlorine and silicon isotope effects

Heavy-atom isotope effects on NMR /sup 1/H chemical shifts have been reported in a few cases but only for second-row elements. The authors now show that /sup 37/Cl//sup 35/Cl isotope effects on the /sup 1/H chemical shifts in chlorinated methanes are about +0.2 ppb (ca. 0.1 Hz at 500 MHz) and that the /sup 29/Si//sup 28/Si isotope effect on the /sup 1/H chemical shift in tetramethylsilane (TMS) is +0.06 +/- 0.01 ppb. It is likely that previously unreported splittings arising from heavy-atom isotope effects will be observable in the /sup 1/H NMR spectra of other organic compounds, given the excellent resolution of modern high field NMR spectrometers.