Proton and 19F Magnetic Resonance of Partially Oriented Fluoromethanes

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.