Which of the following statement is not correct for sigma and pi- bonds formed between two carbon atoms ?

Options

A. Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond
B. Sigma bond determines the direction between carbon atoms but a pi-bond has no primary effect in this regard
C. Sigma bond is stronger than a pi-bond
D. Bond energies of sigma and pi-bonds are of the order of 264 kJ/mol and 347 kJ/mol respectively.

Explanation

To determine which statement is not correct regarding sigma and pi bonds formed between two carbon atoms, let's analyze each option step by step.

### Step 1: Understand Sigma and Pi Bonds
- **Sigma Bonds (σ)**: Formed by the head-on overlap of atomic orbitals. They allow for free rotation around the bond axis.
- **Pi Bonds (π)**: Formed by the sidewise overlap of p orbitals. They restrict rotation due to their lateral overlap.

### Step 2: Analyze Each Statement
1. **Free rotation of atoms above sigma bond is allowed but not in case of pi bond.**
- This statement is **correct**. Sigma bonds allow for free rotation, while pi bonds do not.

2. **Sigma bond determines the direction between the carbon atoms but pi bond has no primary effect on this regard.**
- This statement is **correct**. Sigma bonds define the molecular geometry, while pi bonds do not affect the direction.

3. **Sigma bond is stronger than pi bond.**
- This statement is **correct**. Sigma bonds are generally stronger than pi bonds due to the nature of their overlap.

4. **Bond energies of sigma and pi bonds are in order of that is sigma bond having a 264 and pi bond having a 347 kilojoule per mole respectively.**
- This statement is **not correct**. The bond energy of a sigma bond is typically higher than that of a pi bond. The values given (264 kJ/mol for sigma and 347 kJ/mol for pi) contradict the established understanding that sigma bonds are stronger.

### Conclusion
The statement that is **not correct** is: **"Bond energies of sigma and pi bonds are in order of that is sigma bond having a 264 and pi bond having a 347 kilojoule per mole respectively."**

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