Direct measurement of the distance between adjacent guest molecules in a disordered solid inclusion compound using solid-state F-19-H-1 NMR spectroscopy

Three solid-state NMR techniques have been used to determine the effective average intermolecular F-19,F-19 dipolar interaction, [D'], between fluorine nuclei in neighbouring guest molecules in the 1,10-difluorodecane/urea inclusion compound using a static sample. An MREV8 pulse sequence was used to isolate the shielding powder pattern. A Carr-Purcell-Meiboom-Gill experiment was employed to obtain the dipolar powder pattern. To confirm the results, the full powder pattern influenced by both interactions was obtained and simulated by computer. In all experiments efficient proton decoupling was used. The value of [D'] obtained is 1.01 kHz. This is discussed in relation to the conformations and mutual orientation of the end-groups of the guest molecules. The result is consistent with random distribution over all mutual orientations of the gauche-gauche and gauche-trans situations, with little or no population in the trans-trans form.