title: Resolution of 13C-19F interactions in the 13C NMR of spinning solids and liquid crystals.
abstract: Anomalous line-broadenings of carbon resonances close to 19F have commonly been reported in the 13C NMR of liquid crystals and solids. We have previously shown that these effects in static liquid-crystal samples are related to the difficulty of 1H decoupling in the presence of strong 1H-19F dipolar interactions. We here extend this work to spinning samples (both liquid crystals and solids). A number of different line-broadening mechanisms are elucidated: analogous decoupling effects, magic angle misset, and 19F lifetime-broadening. In relatively mobile systems, such as liquid crystals or soft solids, the limiting factor on 13C resolution (and the ability to directly quantify the 13C-19F interactions) is found to be the efficiency and robustness of the 1H-decoupling. In rigid solids, the lifetime of the 19F spin-states is found to be an additional critical factor.
authors.affiliation: Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Antonioli
authors.forename: Paul
authors.initials: P
authors.lastname: Hodgkinson