Abstract
Intermolecular scalar hyperfine coupling between unpaired electron orbitals and 19F nuclei has been studied in solutions of free radicals in substituted pentafluorobenzenes. Dynamic nuclear polarisation experiments in a weak magnetic field and at various temperatures have shown that both the strength of the intermolecular interaction and the range, depend sensitively upon the π-electron distribution of the aromatic system. The amount of scalar coupling increases with substitution in the sequence H, CH3 , J, Br, CI, F, CN and with the kind of radicals in the order TTBP, DPPH and BDPA.

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