Which of the following compounds will show geometrical isomerism?

Question

Accepted Answer

Option 3, 1-Phenyl propene, is the correct answer because it can exhibit geometrical isomerism due to the presence of a double bond with different substituents on each carbon atom involved in the double bond. Geometrical isomerism, also known as cis-trans isomerism, occurs when there is restricted rotation around a double bond and the substituents attached to the carbon atoms of the double bond are different.

1. **Explanation for Option 3 (1-Phenyl propene):**
   - In 1-Phenyl propene, the double bond is between the first and second carbon atoms. The first carbon is attached to a phenyl group and a hydrogen atom, while the second carbon is attached to a methyl group and a hydrogen atom. Since the substituents on each carbon of the double bond are different, this compound can exist in two geometrical isomers: one where the phenyl and methyl groups are on the same side (cis) and one where they are on opposite sides (trans).

2. **Explanation for why other options are incorrect:**

- **Option 1 (1-Butene):**
     - 1-Butene has a double bond between the first and second carbon atoms. The first carbon is attached to two hydrogen atoms, and the second carbon is attached to a methyl group and a hydrogen atom. Since the first carbon has identical substituents (two hydrogens), 1-butene cannot exhibit geometrical isomerism.

- **Option 2 (Propene):**
     - Propene has a double bond between the first and second carbon atoms. The first carbon is attached to two hydrogen atoms, and the second carbon is attached to a methyl group and a hydrogen atom. Similar to 1-butene, the presence of identical substituents (two hydrogens) on the first carbon prevents propene from showing geometrical isomerism.

- **Option 4 (2-Methyl-2-butene):**
     - In 2-Methyl-2-butene, the double bond is between the second and third carbon atoms. Both of these carbons are attached to identical groups (two methyl groups on the second carbon and a methyl and a hydrogen on the third carbon), which means there is no possibility of geometrical isomerism due to the lack of different substituents on each carbon of the double bond.

In conclusion, 1-Phenyl propene is the only compound among the given options that can exhibit geometrical isomerism due to the presence of different substituents on each carbon atom involved in the double bond.