In alkenes, `pi` -electrons forming carbon-carbon `pi`-bond are

Options

A. localised
B. delocalised over the entire molecule
C. may or may not be delocalised
D. none of the above

Answer

To solve the question regarding the nature of pi electrons in alkenes, we can break down the analysis step by step:

### Step-by-Step Solution:

1. **Understanding Alkenes**:
- Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). The double bond consists of one sigma (σ) bond and one pi (π) bond.

2. **Identifying Pi Electrons**:
- The pi bond is formed by the sideways overlap of p-orbitals from adjacent carbon atoms. The electrons in this bond are referred to as pi electrons.

3. **Localization vs. Delocalization**:
- **Localized Pi Electrons**: These are pi electrons that are confined to a specific bond between two carbon atoms and do not participate in resonance or spread over other parts of the molecule.
- **Delocalized Pi Electrons**: These are pi electrons that can move between multiple atoms, typically seen in conjugated systems where there are alternating single and double bonds.

4. **Analyzing Examples**:
- **Example 1**: In a molecule like buta-1,3-diene (CH2=CH-CH=CH2), the pi electrons can be delocalized. The double bonds can interact, allowing the pi electrons to be shared across multiple carbon atoms.
- **Example 2**: In a simple alkene like butene (CH2=CH-CH2-CH3), the pi electrons are localized between the two carbon atoms involved in the double bond, as there are no other pi bonds to allow delocalization.

5. **Conclusion**:
- From the analysis, we see that in alkenes, the pi electrons can either be localized (as in butene) or delocalized (as in buta-1,3-diene). Therefore, the correct answer to the question is that the pi electrons forming carbon-carbon pi bonds in alkenes "may or may not be delocalized."

### Final Answer:
The correct option is C: "may or may not be delocalized."