Editing Lewisite (section)

==Chemical composition==
Lewisite can be a mixture of molecules with a different number of vinylchloride groups on the arsenic chloride: lewisite itself (2-chlorovinylarsonous dichloride), along with ''bis''(2-chlorovinyl)arsinous chloride ([[lewisite 2]]) and ''tris''(2-chlorovinyl)arsine ([[lewisite 3]]).<ref>{{cite book |last1= McNutt |first1= Patrick M. |last2= Tracey L. |first2= Hamilton |chapter= Ocular toxicity of chemical warfare agents |title= Handbook of Toxicology of Chemical Warfare Agents |publisher= Academic Press |year= 2015 |pages= 535–555 }}</ref> In addition, there are sometimes isomeric impurities: lewisite itself is mostly [[Cis–trans isomerism|''trans'']]-2-chlorovinylarsonous dichloride, but the ''cis'' stereoisomer and the [[constitutional isomer]] (1-chlorovinylarsonous dichloride) may also be present.<ref name="Urban1999">{{cite journal |title= Conformational analysis of the isomers of lewisite |first1= Joseph J. |last1= Urban |first2= Robert L. |last2= von Tersch |journal= J. Phys. Org. Chem. |volume= 12 |pages= 95–102 |year= 1999 |issue= 2 |doi= 10.1002/(SICI)1099-1395(199902)12:2<95::AID-POC91>3.0.CO;2-V |doi-access= free }}</ref>

Experimental and computational studies both find that the ''trans''-2-chloro isomer is the most stable, and that the carbon–arsenic bond has a [[Conformational isomerism|conformation]] in which the [[lone pair]] on the arsenic is approximately aligned with the vinyl group.<ref name="Urban1999"/>