Guest dynamics in carceplexes: a 2H NMR study
|Title||Guest dynamics in carceplexes: a 2H NMR study|
|Author(s)||N. Chopra, R. G. Chapman, Y. F. Chuang, J. C. Sherman, E. E. Burnell, James M. Polson|
|Journal||Journal of the Chemical Society-Faraday Transactions|
|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.|
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