Nuclear Spin—Spin Coupling Involving Heavy Nuclei. The Coupling between Hg199 and H1 Nuclei in CH3HgX and CH3CH2HgX Compounds

Abstract

Nuclear spin coupling between protons and Hg199 nuclei in CH3HgX and CH3CH2HgX compounds has been investigated. As the X substituent is made more electronegative very large increases in the spin‐coupling constant up to 2½‐fold were observed. Smaller alterations occur in different solvent media, and alkyl exchange could be observed in several compounds. In the CH3CH2HgX compounds the changes in the spin‐coupling constants of the Hg nucleus with the protons in the methylene group and in the methyl group are comparable in magnitude. The results are interpreted in terms of a simplified model for contact interaction employing optical hyperfine structure (hfs) constants. Qualitative arguments are employed to assess the relative importance of other coupling mechanisms. It is concluded that spin coupling arising from electron orbital motion is negligible, and while dipole—dipole contributions may be important, the evidence indicates the Fermi contact interaction is the dominant coupling mechanism.