Molecular motion/dynamics, solid-state relaxation time measurements

Molecular Motions and Dynamic Structures. Molecular motions are of quite general occurrence in the solid state for molecules of high symmetry (22,23). If the motion does not introduce disorder into the crystal lattice (as, for example, the in-plane reorientation of benzene which occurs by 60° jumps between equivalent sites) it is not detected by diffraction measurements which will find a seemingly static lattice. Such molecular motions may be detected by wide-line proton NMR spectroscopy and quantified by relaxation-time measurements which yield activation barriers for the reorientation process. In addition, in some cases, the molecular reorientation may be coupled with a chemical exchange process as, for example, in the case of many fluxional organometallic molecules. ... 

In addition to spin relaxation, there are the methods that measure molecular motion. The spectra reflecting the quadrupolar interaction are sensitive to the mid-range of frequencies. Therefore, NMR spectroscopy is a powerful tool to examine the molecular motion of polymers in the solid state. Different types of motion can be di.scriminated on the basis of their time scale and their exchange geometry. The one-dimensional quadrupole echo lineshape of "H NMR is sensitive to dynamics in the range 10 s < r < 10 s. where is the... 

Molecular dynamics studies in chiral smectic liquid-crystalline phases by solid-state NMR measurements have been reported. The temperature dependence of the spin-lattice relaxation time Ti was investigated. For the aliphatic carbons in a flexible chain the value of Ti was found to increase with increasing temperature, because the molecular motion characterised by Xc was faster than the Larmor frequency coq-... 

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