Can a `sigma` bond be formed in the absence of `pi` bond ?

Answer

### Step-by-Step Solution:

1. **Understanding Sigma and Pi Bonds**:
- Sigma (σ) bonds are formed by the head-on overlap of atomic orbitals. They are the first bonds formed between two atoms.
- Pi (π) bonds are formed by the sidewise overlap of p-orbitals and are typically found in double and triple bonds.

2. **Existence of Sigma Bonds**:
- Sigma bonds can exist independently without the presence of pi bonds. This is because they are formed through the direct overlap of orbitals, which does not require the additional sidewise overlap that pi bonds do.

3. **Example of Ethane (C₂H₆)**:
- Consider the molecule ethane (C₂H₆). The structure of ethane consists of two carbon atoms bonded to each other and to hydrogen atoms.
- The bonding in ethane involves only single bonds, which are all sigma bonds.

4. **Counting the Bonds in Ethane**:
- In ethane, there are a total of 7 sigma bonds:
- 1 sigma bond between the two carbon atoms.
- 6 sigma bonds between each carbon atom and the three hydrogen atoms attached to it.
- There are no pi bonds present in ethane since it only contains single bonds.

5. **Conclusion**:
- Therefore, it is confirmed that sigma bonds can exist without pi bonds, as demonstrated by the example of ethane, which contains only sigma bonds.