It is shown that the absolute sign of the indirect proton–fluorine nuclear spin–spin coupling constant JHF is positive in the fluoromethanes from their spectra in the nematic liquid crystal p,p′-di-n-hexyloxyaz-oxybenzene and the knowledge of the previously determined absolute signs of the 19F magnetic shielding anisotropies in CH3F and CHF3. Values of the 19F and proton magnetic shielding anisotropies are determined and the problems of shift referencing are discussed. If it is assumed that the contributions to magnetic shielding of the H and F nuclei are axially symmetric about the respective C–H and C–F bonds, the experimental values can be transformed into magnetic shielding anisotropies along bond directions.
Articles you may be interested inDetermination of the electric quadrupole moment of 7Li by Coulomb scattering of an aligned 7Li beam AIP Conf. Proc. 69, 991 (1981);The 'lLi magnetic resonance in polycrystalline methyllithium-da and ethyllithium-d. was examined at room temperature and at 77°K. The 7Li quadrupole coupling parameters were determined from the quadrupole fine structure of the 'lLi magnetic resonance to be 1 e 2 qQlh 1 =48 kclsec and ' 1 = 0 for methylithium-da and I e2qQlh 1=83 kclsec and '1=0.79 for ethyllithium-d5. The quadrupole coupling is independent of temperature for ethyllithium-d5, but the temperature dependence of the coupling is uncertain for methyllithium-da because of the difficulties in observing the resonance at 77°K. At room temperature the 7Li magnetic resonance of ethyllithium-d. exhibits a narrow component, 87 cps broad, superimposed upon the broad, quadrupolar split line. This sharp component, which is similar to that observed in isopropyllithium, t-butyllithium, and neopentyllithium, is not observed at 77°K and is presumably due to motional narrowing. The 7Li resonance of methyllithium-da displayed no sharp component at room temperature, being like allyllithium, propynyllithium, phenyllithium, fluorenyllithium, and alkoxylithium compounds in this respect.
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