2-butene shows geometrical isomerism due to:

Options

A. Restricted rotation about double bond
B. Free rotation about double bond
C. Free rotation about single bond
D. Chiral carbon

Answer

To determine why 2-butene shows geometrical isomerism, we can follow these steps:

### Step 1: Understand the Structure of 2-Butene
2-butene is an alkene with the molecular formula C4H8. Its structure can be represented as follows:
- The carbon chain consists of four carbon atoms.
- The double bond is located between the second and third carbon atoms.

### Step 2: Identify the Nature of the Double Bond
In alkenes, the presence of a double bond (C=C) restricts the rotation around that bond. This is a key factor in the formation of geometrical isomers.

### Step 3: Recognize the Requirement for Geometrical Isomerism
For geometrical isomerism to occur, the double-bonded carbons must have different substituents. In 2-butene, the second carbon (C2) has a methyl group (CH3) and a hydrogen atom (H), while the third carbon (C3) also has a methyl group (CH3) and a hydrogen atom (H). This means that the groups attached to the double bond are not identical, allowing for different spatial arrangements.

### Step 4: Draw the Geometrical Isomers
1. **Cis Isomer**: In the cis isomer, the two methyl groups (CH3) are on the same side of the double bond.
- Structure:
```
CH3 CH3
\ /
C = C
/ \
H H
```

2. **Trans Isomer**: In the trans isomer, the two methyl groups (CH3) are on opposite sides of the double bond.
- Structure:
```
CH3 H
\ /
C = C
/ \
H CH3
```

### Step 5: Conclusion
The geometrical isomerism in 2-butene arises due to the restricted rotation around the double bond, which allows for the formation of two distinct isomers: cis and trans.

### Final Answer
2-butene shows geometrical isomerism due to restricted rotation about the double bond.

---