Answer
Geometric (Cis-Trans) Isomerism
Geometric isomerism, also known as cis-trans isomerism, occurs due to restricted rotation around a double bond or within a ring structure. For this type of isomerism to exist, two conditions must be met:
- There must be restricted rotation (e.g., a double bond or ring system).
- Each of the atoms involved must have two different substituents.
Pent-1-ene and 2-methylhex-2-ene do not show geometric isomerism because they possess identical groups on one of the double-bonded carbon atoms.
1,1-Dimethylcyclopropane also cannot exhibit cis-trans isomerism, as both methyl groups are on the same carbon atom.
In 1,2-dimethylcyclohexane, the methyl groups on C-1 and C-2 can occupy either the same face (cis) or opposite faces (trans) of the ring, resulting in distinct geometric isomers.