Editing Disulfide (section)

===Structure===
Disulfides have a C–S–S–C [[dihedral angle]] approaching 90°.  The S–S bond length is 2.03 Å in [[diphenyl disulfide]],<ref>{{cite journal|doi=10.1107/S0567740869005188 |title=The Crystal Structure of Diphenyl Disulphide |date=1969 |last1=Lee |first1=J. D. |last2=Bryant |first2=M. W. R. |journal=Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry |volume=25 |issue=10 |pages=2094–2101 |bibcode=1969AcCrB..25.2094L }}</ref>  similar to that in elemental sulfur.

Disulfides are usually symmetric but they can also be unsymmetric. Symmetrical disulfides are compounds of the formula {{chem2|RSSR}}. Most disulfides encountered in organosulfur chemistry are symmetrical disulfides.  '''Unsymmetrical disulfides''' (also called '''heterodisulfides''' or '''mixed disulfides''') are compounds of the formula {{chem2|RSSR'}}.  Unsymmetrical disulfide are less common in organic chemistry, but many disulfides in nature are unsymmetrical.  Illustrative of a symmetric disulfide is [[cystine]]. 

====Cyclic disulfides====
Disulfides can be components of rings.  [[Lipoic acid]], a [[1,2-Dithiolane|1,2-dithiolane]] is a major example.  Rings with more than one disulfide usually tend to polymerize.<ref>{{cite journal |doi=10.1016/0040-4020(89)80036-5 |title=Characterization and stability of cyclic disulfides and cyclic dimeric bis(disulfides) |date=1989 |last1=Houk |first1=Janette |last2=Whitesides |first2=George M. |journal=Tetrahedron |volume=45 |pages=91–102 }}</ref>

====Other specialized organic disulfides====
[[Thiuram disulfide]]s, with the formula (R<sub>2</sub>NCSS)<sub>2</sub>, are disulfides but they behave distinctly because of the [[thiocarbonyl]] group.