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Very often, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. [4] When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans.
cis-DCE, the Z isomer, is obtainable by the controlled chlorination of acetylene: C 2 H 2 + Cl 2 → C 2 H 2 Cl 2. Industrially both isomers arise as byproducts of the production of vinyl chloride, which is produced on a vast scale. Unlike 1,1-dichloroethylene, the 1,2-dichloroethylene isomers do not polymerize. [1]
Traditionally, double bond stereochemistry was described as either cis (Latin, on this side) or trans (Latin, across), in reference to the relative position of substituents on either side of a double bond. A simple example of cis–trans isomerism is the 1,2-disubstituted ethenes, like the dichloroethene (C 2 H 2 Cl 2) isomers shown below. [7]
This salt is less soluble than its dull-green isomer trans-dichlorobis(ethylenediamine)cobalt(III) chloride. This pair of isomers were significant in the development of the area of coordination chemistry. [3] The chiral cis isomer is obtained by heating the trans isomer.
The two isomers are extremely difficult to separate by distillation because of the proximity of their boiling points (~4 °C for cis and ~1 °C for trans [5]). However, separation is unnecessary in most industrial settings, as both isomers behave similarly in most of the desired reactions.
And each of these cis-trans isomers can possibly have stable "chair" or "boat" conformations (although the barriers between these are significantly lower than those between different cis-trans isomers). The two isomeric complexes, cisplatin and transplatin, are examples of square planar MX 2 Y 2 molecules with M = Pt.
1,2-Dimethylcyclopropane is a cycloalkane consisting of a cyclopropane ring substituted with two methyl groups attached to adjacent carbon atoms. [1] It has three stereoisomers, one cis-isomer and a pair of trans-enantiomers, which differ depending on the orientation of the two methyl groups.
The relative amount of each isomer in the polymer is dependent on the mechanism of the polymerization reaction. [citation needed] Anionic chain polymerization, which is initiated by n-Butyllithium, produces cis-1,4-polyisoprene dominant polyisoprene. 90–92% of repeating units are cis-1,4-, 2–3% trans-1,4- and 6–7% 3,4-units. [3]