Accession Number : AD0284918

Title :   FLUORINE NUCLEAR MAGNETIC RESONANCE SHIELDING IN META SUBSTITUTED FLUOROBENZENES. THE EFFECT OF SOLVENT ON THE INDUCTIVE ORDER

Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK

Personal Author(s) : TAFT,ROBERT W. ; PRICE,ELTON

Report Date : AUG 1962

Pagination or Media Count : 1

Abstract : The F-19 NMR shielding parameters for 21 meta substituted fluorobenzenes relative to a fixed external standard and relative to fluorobenzene as an internal standard were obtained at room temperature at high dilution in 20 widely varying pure solvents. Extensive measurements with 24 additional substituent groups in non-polar and in hydroxylic solvents, both pure and mixed, wereALSO MADE. In spite of a variation over 9.2 ppm in shielding for a given fluorobenzene relative to the fixed external standard, the shielding parameters for seven compounds with chemically inert meta substituents relative to internal fluorobenzene are solvent invariant to a precision of the same order as experimental error. This result offers critical evidence that intermolecular shielding resulting from interaction of the F atom with solvent makes little or no contribution to the shielding parameter of a meta substituted fluorobenzene relative to fluorobenzene as the internal standard. A further conclusion is that the field effect makes no practical contribution to the variation in shielding due to meta (and presumably para) substituents. It is further implied that the bond dipole moments of groups are independent to good precision of this variation in dielectric constant for many nonprotonic solvents at room temperatures. The effects of solvent on the shielding parameter of meta substituted fluorobenzenes with chemically active substituents is attributed to charge-transfer solvent-substituent interactions. (Author)

Descriptors :   *BENZENES, *FLUORIDES, *NUCLEAR MAGNETIC RESONANCE, SHIELDING, SOLVENT ACTION

Distribution Statement : APPROVED FOR PUBLIC RELEASE