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Schlagwörter:
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Zusammenfassung:
The fluorine and proton magnetic shielding tensors of 4,4′-difluorobiphenyl have been determined at 89·3 and 93 MHz, respectively. Heteronuclear decoupling was applied during a WAHUHA multiple pulse sequence in an effort to suppress heteronuclear H-F dipolar couplings in addition to homonuclear dipolar couplings. Principal values of the almost completely asymmetric fluorine shielding tensor are σ xx F = -107·4 ± 0·4, σ yy F = -49·3 ± 0·4 and σ zz F = -0·7 ± 0·4 p.p.m. relative to liquid hexafluorobenzene.
The proton data could be analysed to yield two different sets of principal shielding values: σ xx I = -1·5 ± 1·5, σ yy I = -6·5 ± 1·5, σ zz I = -11·5 ± 1·5 p.p.m. and σ xx II = -5·5 ± 1·5, σ yy II = -7·5 ± 1·5 and σ zz II = - 9·5 ± 1·5 p.p.m. relative to TMS.
The crystal structure of 4,4′-difluorobiphenyl has not yet been determined. As part of this work we determined its space group. Proton dipolar interactions (from wide line spectra) and 19F principal shielding directions were used to determine the orientation of the molecules in the unit cell and to ascertain that the molecules are planar in the crystal.
