37Cl/35Cl and 13C/12C isotope effects on the fluorine shielding in several two-carbon chlorofluorocarbons

✍ Scribed by Marc Tordeux; Claude Wakselman; Olivier Jarjayes; Claude G. Béguin

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 190 KB
• Volume: 39
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.846

✦ Synopsis

Abstract

Isotope effects on the chemical shift (IECS) of ^19^F bonded through two or three bonds to the isotopes ^35^Cl and ^37^Cl are reported for a wide range of two‐carbon chlorofluorocarbons (and, for a few cases, with the isotopes ^79^Br and ^81^Br, for two‐carbon bromofluorocarbons). These IECS through two bonds were found to range, for one chlorine atom, from −5.0 to −7.6 ppb for aliphatic compounds and from −4.5 to −6.4 ppb for olefinic compounds. The IECS through three bonds were found to be less than −1.15 ppb. No deviation from additivity was detected for the IECS when several equivalent chlorine atoms are present. The broadening of the ^19^F lines, due to scalar relaxation arising from ^19^F–^37/35^Cl spin–spin interactions, ranges from 0.32 to 2.50 Hz in our series and are related to the ^2^J(Cl, ^19^F)T~1~(Cl) term. IECS of ^19^F bonded through one or two bonds to the isotopes ^13^C and ^12^C are also reported for the same series. Several correlations, related to structural information, can be made and discussed between these IECS [^13/12^C IECS through two bonds as a function of ^1^J(^13^C, ^19^F) spin–spin coupling constants and ^13/12^C IECS as a function of ^37/35^Cl IECS]. ^37/35^Cl IECS can also be observed on ^13^C satellites of ^19^F spectra. For non‐symmetrical compounds, the dependence of these signals on the ^37/35^Cl IECS is the same as that for the main ^19^F signal; however, for the centrosymmetrical compounds, the main ^19^F signal appears to be sensitive to all the chlorine atoms, whereas the ^13^C satellites seem to be sensitive only to the directly bonded chlorine. Copyright © 2001 John Wiley & Sons, Ltd.