Line-splitting and broadening effects from 19F in the 13C NMR of liquid crystals and solids

The NMR resonances of 13C spins in proximity to 19F are often unusually broad, degrading resolution and limiting the ability to quantify the C–F interactions. We observe line-splittings and selective broadenings in a liquid crystal sample that strongly depend on the 1H decoupling. We propose a simple rationalisation that successfully reproduces the experimental behaviour, and find that suitably adapted decoupling sequences effectively eliminate the line-broadenings. Experiments on solid samples show similar variations with decoupling sequence, and the same effects may be general to H–X–Y systems.