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GUEST DYNAMICS IN CARCEPLEXES - A H-2 NMR-STUDY

TitleGUEST DYNAMICS IN CARCEPLEXES - A H-2 NMR-STUDY
Publication TypeJournal Article
Year of Publication1995
AuthorsChopra, N, Chapman, RG, Chuang, YF, Sherman, JC, Burnell, EE, Polson, JM
JournalJournal of the Chemical Society-Faraday Transactions
Volume91
Pagination4127-4131
Date PublishedNov
Type of ArticleArticle
ISBN Number0956-5000
Keywordsbenzene, COMPLEXATION, MOTIONS, RESONANCE LINE-SHAPES, SOLIDS, SPECTROSCOPY
Abstract

Solid-state H-2 NMR powder spectra and T-1 longitudinal relaxation data have been collected for carceplexes containing benzene and acetonitrile guest molecules. Analysis of the data suggests that benzene rotates rapidly about its C-6 axis with an activation energy of 25.8 +/- 0.4 kJ mol(-1). In addition, it reorients about the C-4 axis of the carceplex cavity with a rate (ca. 10(6)-10(7) s(-1)) that is in the intermediate regime on the H-2 NMR spectral timescale in the temperature range T = 310-400 K. Lineshape simulations suggest that this reorientation has less than four-fold symmetry owing to unequal site populations, probably a reflection of the deviation from C-4 symmetry of the carceplex geometry. Acetonitrile reorients rapidly (much greater than 10(5) s(-1)) about a four-fold symmetric axis for T greater than or equal to 181 K.

URL<Go to ISI>://A1995TF18600015