Define restricted rotation and give on example each of acyclic and cyclic compound, which can show geometrical isomersm.

Answer

### Step-by-Step Text Solution:

**Step 1: Define Restricted Rotation**
Restricted rotation refers to the limitation of the free rotation around a bond, typically due to the presence of a double bond or a cyclic structure. This restriction occurs because of the high energy barrier that prevents the rotation from occurring freely between different conformations.

**Step 2: Example of a Cyclic Compound Showing Geometrical Isomerism**
An example of a cyclic compound that exhibits geometrical isomerism is 1,2-dibromocyclopentane. In this compound, the two bromine atoms can be positioned either on the same side of the ring (cis isomer) or on opposite sides (trans isomer).

- **Cis Isomer**: Both bromine atoms are on the same side of the cyclopentane ring.
- **Trans Isomer**: The bromine atoms are on opposite sides of the cyclopentane ring.

The restricted rotation around the carbon-carbon bonds in the ring prevents the easy interconversion between these two isomers.

**Step 3: Example of an Acyclic Compound Showing Geometrical Isomerism**
An example of an acyclic compound that can show geometrical isomerism is 2-butene. In 2-butene, the two methyl groups can either be on the same side (cis isomer) or on opposite sides (trans isomer) of the double bond.

- **Cis Isomer**: The two methyl groups are on the same side of the double bond.
- **Trans Isomer**: The two methyl groups are on opposite sides of the double bond.

The presence of the double bond creates a restriction to rotation, resulting in distinct geometrical isomers.