Barrier height pseudorotation

An especially interesting situation is found in the field of heterocycles containing more than one sulfur atom. Here two different relatively stable conformations (f.i. chair and twist-boat form) have often been detected in the NMR-spectra they are intercon-verted by two processes (version and pseudorotation) which differ significantly in the height of their energy barrier. In a few cases the mobile heterocycles crystallize in only one of these conformations. 

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