In chemistry,<unk>  or geometric<unk>  is a form of stereoisomerism describing the orientation of functional groups within a molecule. Such isomers typically contain double bonds which cannot rotate, but they can also arise from ring structures where the rotation of bonds is greatly restricted.
The term "geometric<unk> " is considered an obsolete synonym of<unk> " by IUPAC. It is sometimes used as a synonym for general stereoisomerism (e.g. optical<unk>  being called geometric<unk> ; the correct term for non-optical stereoisomerism is diastereomerism.
There are two forms of a<unk><unk>  isomer, the<unk>  and<unk>  versions. When the substituent groups are oriented in the same direction the diastereomer is referred to as<unk> ,  while when the substituents are oriented in opposing directions the diastereomer is referred to as<unk> . An example of a small hydrocarbon displaying<unk>  is 2-butene.
Alicyclic compounds can also display<unk> . As an example of a geometric isomer due to a ring structure, consider 1,2-dichlorocyclohexane:
Cis-trans isomerism
Stereoisomerism
Conformational isomerism
Thermal depolymerization
Degenerate energy level
Allosteric regulation
Fischer esterification
Nuclear isomer