Calculation of some fluorine nuclear screening constants

✍ Scribed by K. A. K. Ebraheem; G. A. Webb

• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: English
• Weight: 353 KB
• Volume: 10
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270100118

✦ Synopsis

Abstract

The ^19^F screening constants and their anisotropies have been calculated for 50 fluorine molecular environments. The calculations have been performed within a framework in which gauge‐dependent atomic orbitals are used in the molecular orbital description. Calculations employing both INDO and CNDO/S standard parameterizations are reported. The molecules considered include simple binary fluorides and fluorocarbons. Both sets of calculations provide reasonable accounts of the ^19^F screening data for the binary fluorides. The presence of electric field effects in the aliphatic fluorocarbons are not accounted for by the present calculations. In the conjugated fluorocarbons the gross ^19^F chemical shift trend is reproduced except for ortho fluorines where electric field contributions are significant. The most highly screened component of σ is calculated to lie along the CF bond of various fluorobenzenes but perpendicular to the plane of 4,4′‐difluorobiphenyl, in agreement with experiment.