Sulfur rotational isomerism

The rotational isomerism that probably exists in solution may be responsible for the fact that so far no single crystals have been obtained for organic polysulfanes with more than nine sulfur atoms in a chain. However, cyclic polysulfanes with up to 11 neighboring sulfur atoms have been structurally elucidated (see below), and the structures of homocyclic sulfur molecules with up to 20 atoms are known. ... 

Van Wart, H. E. and Scheraga, H. A. (1976a). Raman spectra of cystine-related disulfides. Effect of rotational isomerism about carbon-sulfur bonds on sulfur-sulfur stretching frequencies. J. Phys. Chem., 80, 1812-22. [225]... 

The different conformations of molecular sulfur in the eight- and six-membered rings and in the extended helixes are examples of rotational isomerism, encountered also in derivatives. The all-ws configuration of S6 and S8 transforms into the all-lrans of the helixes on breaking of a bond and rotation of approximately 180° about the symmetrically located bond. 

The nonplanarity of sulfur chains gives rise to rotational isomerism, namely, to two enantiomorphs of a disulfide, two forms of a trisulfide of which one is a pair of enantiomorphs, and to three pairs of enantiomorphs of a tetrasulfide. In gases and solutions, equilibrium mixtures probably... 

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