Optical IsomerismFigure 78 Trans-2-butene
There are two forms of these isomers; thecisandtransversions. The form in which the
substituent hydrogen atoms are on the same side of the bond that doesn’t allow rotation
is calledcis; the form in which the hydrogens are on opposite sides of the bond is called
trans. An example of a small hydrocarbon displaying cis-trans isomerism is 2-butene.
Alicyclic compounds can also display cis-trans isomerism. As an example of a geometric
isomer due to a ring structure, consider 1,2-dichlorocyclohexane:
30.2 Optical Isomerism
Main article:Chirality^2
Optical isomers are stereoisomers formed when asymmetric centers are present, for example,
a carbon with four different groups bonded to it. Enantiomers are two optical isomers (i.e.
isomers that are reflections of each other). Every stereocenter in one isomer has the opposite
configuration in the other.
2 Chapter 32 on page 129