Geometrical Isomerism in Alkenes

Introduction:
Geometrical isomerism is a type of stereoisomerism that occurs in compounds with restricted rotation around a double bond. It arises due to the presence of different groups or atoms on the same side or opposite sides of the double bond. Alkenes, which contain a carbon-carbon double bond, can exhibit geometrical isomerism.

Explanation:
In the given options, the alkene that exhibits geometrical isomerism is option B, 2-butene. Let's understand why.

1. Definition of Geometrical Isomerism:
Geometrical isomerism occurs when different groups or atoms are arranged differently around a double bond, resulting in different spatial arrangements of the molecule.

2. Structure of 2-Butene:
2-Butene is an alkene with four carbon atoms and one double bond. Its structure can be represented as CH3-CH=CH-CH3. Here, the double bond is between the second and third carbon atoms.

3. Identification of Geometrical Isomers:
To determine if an alkene exhibits geometrical isomerism, we need to check if there are different groups attached to the double bond and if they are arranged differently on the same or opposite sides of the bond.

In 2-butene, the two groups attached to the double bond are methyl (CH3) groups. These groups can be arranged in two ways:
- The two methyl groups can be on the same side of the double bond, resulting in the cis-isomer.
- The two methyl groups can be on opposite sides of the double bond, resulting in the trans-isomer.

4. Explanation of Geometrical Isomers:
In the cis-isomer of 2-butene, the two methyl groups are on the same side of the double bond. This arrangement creates a steric hindrance because the bulky methyl groups are close to each other. The cis-isomer is less stable due to this steric hindrance.

In the trans-isomer of 2-butene, the two methyl groups are on opposite sides of the double bond. This arrangement minimizes steric hindrance, resulting in a more stable molecule.

5. Conclusion:
Among the given options, only 2-butene (option B) exhibits geometrical isomerism. The presence of different groups (methyl groups) on the same or opposite sides of the double bond allows for the formation of cis- and trans-isomers.

Option B is correct...