A NEW CLASS OF COMPOUNDS SUITED TO STUDY THE TORSIONAL DYNAMICS IN THE QUANTUM REGIME - THE CALIXARENES

Inelastic neutron scattering spectroscopy has been used to study the rotational dynamics of methyl groups in the p-tert butylcalix [4] arene(1:1)toluene complex. The neutron scattering function shows several lines between 0. 16 and 2.6 meV, and can be satisfactorily reproduced by the single-particle model for rotational tunneling only if the presence of inequivalent sites is assumed, in contrast with the crystallographic determinations. An approach consistent with the room-temperature crystal structure and giving a satisfactory description of the experimental results is obtained by the quantum sine-Gordon model, which describes the dynamics of infinite chains of coupled methyl groups.