29/28, 30/28Silicon, 34/32sulfur and 80/77selenium isotope-induced fluorine chemical shifts through two bonds
Résumé
Isotope effects on fluorine chemical shifts induced by heteroatoms bonded covalently to a carbon atom bearing fluorine atoms were studied. For each compound, the isotope-induced chemical shifts 2 19F(X) through two bonds were measured for the heteroatom (X = 29/28Si, 30/28Si, 34/32S and 80/77Se). The 1 19F(13/12C) values for the carbon bonded to the fluorine atoms were also recorded. Examination of the 19F NMR data showed homogeneity of the isotope-induced chemical shifts along the rows of the periodic table and regularity down the columns (from 10 to 15 ppb per mass unit for the second row to 0.4 ppb for the fourth row). It became negligible for atoms of the fifth row.