Geometrical isomerism, also known as cis-trans isomerism or configurational isomerism, is shown by compounds that have restricted rotation around a bond, typically a carbon-carbon double bond (C=C), or by ring compounds where rotation is hindered. For geometrical isomerism to occur:
- The compound must have a double bond (C=C) or a ring structure that restricts rotation.
- Each carbon atom involved in the double bond must have two different groups attached to it.
This restriction leads to different spatial arrangements of the groups, resulting in isomers such as cis (same side) and trans (opposite side) forms. For example, alkenes like but-2-ene exhibit geometrical isomerism because the double bond prevents free rotation and the carbons have different substituents, allowing distinct cis and trans isomers
. In contrast, if the groups attached to the double-bonded carbons are identical or if there is a plane of symmetry, geometrical isomerism does not occur
. In coordination chemistry, geometrical isomerism can also be shown by complexes with coordination number 6 due to specific hybridization (d2sp3), but this is more specialized
. Summary:
- Geometrical isomerism is mainly shown by alkenes (unsaturated organic compounds) with C=C bonds where each carbon has different groups.
- It is also shown by cyclic compounds where rotation is restricted.
- It is characterized by cis-trans or E-Z isomers based on the relative positions of substituents around the double bond or ring
