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| - 13C → 1H Cross-Polarization NMR in Solids at Natural 13C Abundance
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| - We discuss the features of cross-polarization (CP)between dilute spin systems with substantial molecularmotion and discuss the applicability of two different theories for thedescription of cross-polarization in toluene-solvated fullerene-70. The material was examined by 13C→ 1H and 1H → 13C CP NMR withmagic-anglespinning (MAS). 13C → 1H CP was set onperdeuterated glycine. Both solids were at the natural13C isotopicabundance and with ca. 2% 1H content, so that13C and 1H spin species were bothdilute. We have found thatCP between the fullerene carbons and the toluene protons in eitherdirection is not site-specific and its kineticsare governed by the same time constants. This result and themeasured signal intensities are rationalized interms of the short-correlation-time theory of CP. The toluenecarbons cross-polarize only from the adjacentprotons according to the classic CP theory. There are two kinds oftoluene molecules with the relaxationtimeof 10 and 70 ms. Theformer molecules are single and more mobile, and the latter, lessmobile,probably form aggregates. CP between the dilute spin systems isvery sensitive to molecular motion.
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