Unbranched alkenes can form geometric isomers while unbranched alkanes cannot due to the presence of a double bond in alkenes.
1. Alkenes have a double bond between two carbon atoms, which restricts rotation around this bond. This limitation in rotation allows for different spatial arrangements of atoms or groups around the double bond, leading to the formation of geometric isomers.
2. Geometric isomers have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In alkenes, the geometric isomers result from the cis-trans isomerism, where the groups attached to the carbons of the double bond are arranged differently in space.
3. On the other hand, alkanes consist of only single bonds between carbon atoms. Single bonds allow free rotation around the bond axis, so there is no restriction that leads to the formation of geometric isomers in alkanes.
Therefore, the explanation for the ability of unbranched alkenes to form geometric isomers while unbranched alkanes cannot lies in the microscopic domain, specifically in the spatial arrangement of atoms around the double bond.
