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Methyl group tunnelling studies in calixarenes

✍ Scribed by R. Caciuffo; G. Amoretti; C.J. Carlile; F. Fillaux; O. Francescangeli; M. Prager; F. Ugozzoli

Publisher: Elsevier Science
Year: 1994
Tongue: English
Weight: 471 KB
Volume: 202
Category: Article
ISSN: 0921-4526
DOI: 10.1016/0921-4526(94)90306-9

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✦ Synopsis

Inelastic neutron scattering has been used to study the tunnelling of methyl groups belonging to several guest molecules (toluene, p-xylene, 7-picoline) incarcerated in a host calixarene matrix. In all the cases investigated, the low temperature neutron spectra show a number of bands which may be interpreted as being due to transitions between tunnel-split librational states of the guest methyl groups. The main line occurs near 0.63 meV, very close to the CH 3 quantum free rotor limit. In the toluence complex, the quantum regime persists at least up to 60 K. Effects of coupling between rotational and vibrational modes are discussed. Very subtle structural changes not revealed by diffraction measurements are suggested by the neutron spectroscopy results.

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