Question

Hyper conjugation involves (l) delocalization of \(\sigma\) electrons into an adjacent \(\pi\) -bond (2) delocalization of \(\pi\) electrons into an adjacent double bond (3) delocalization of \(\pi\) electrons into an adjacent \(\pi\) -bond (4) All the above are true

Short answer

Hyperconjugation involves the delocalization of \(\sigma\) electrons into an adjacent \(\pi\)-bond.

Step-by-step solution

Understanding Hyperconjugation

Hyperconjugation is known as the interaction of \(\sigma\) electrons with an adjacent empty or partially filled \(p\)-orbital or \(\pi\)-orbital to give an extended molecular orbital. Let's evaluate each statement based on this definition.

Analysis of Statement 1

Statement 1 mentions the delocalization of \(\sigma\) electrons into an adjacent \(\pi\)-bond. This corresponds directly to the definition of hyperconjugation. Hence, Statement 1 is true.

Analysis of Statement 2

Statement 2 mentions the delocalization of \(\pi\) electrons into an adjacent double bond. This does not fit the definition of hyperconjugation, which involves \(\sigma\) electrons. Hence, Statement 2 is false.

Analysis of Statement 3

Statement 3 mentions the delocalization of \(\pi\) electrons into an adjacent \(\pi\)-bond. This also does not align with the definition of hyperconjugation as it involves \(\pi\) electrons instead of \(\sigma\) electrons. Hence, Statement 3 is false.

Conclusion

Since only Statement 1 is true and Statements 2 and 3 are false, the correct answer is not 'All the above are true'. The correct answer must be assessed based only on the statements individually.

Key concepts

delocalization of sigma electrons

Hyperconjugation primarily involves the delocalization of \(\sigma\) electrons. This means that the electrons in a \(\sigma\)-bond, typically found in a C-H or C-C bond, interact with an adjacent \(\pi\)-system or empty orbital. Instead of being confined to the \(\sigma\)-bond, these electrons spread out or 'delocalize'. This spreading out helps to stabilize the molecule by reducing electron density in a single area.
Such delocalization can contribute significantly to the stability of carbocations, alkenes, and other similar structures.

• For example, in a simple alkene like propene, the \(\sigma\)-electrons of a C-H bond adjacent to the double bond will delocalize into the \(\pi\)-orbital.
• This effect is sometimes referred to as 'no-bond resonance' because it gives the molecule a resonance structure without the formation of a new bond.

adjacent pi-bond

Hyperconjugation involves interaction with an adjacent \(\pi\)-bond, which is crucial to the delocalization process. A \(\pi\)-bond is found in double and triple bonds, where electrons are not found directly between the atoms but above and below the plane of the atoms due to the sideways overlap of p orbitals.
When a \(\sigma\)-electron pair from, say a C-H bond, interacts with this \(\pi\)-bond, it helps in stabilizing the overall structure.
This stabilization is because the \(\sigma\)-bond electrons are now 'shared' in the vicinity of the more stable \(\pi\)-bond electron cloud, spreading the electrons out over a larger volume of space.

• In molecular orbital theory terms, the \(\sigma\)-electrons mix with the \(\pi\)-orbital, forming new delocalized molecular orbitals.
• This results in an overall stabilization due to the delocalization of electrons over a wider area.

molecular orbital interaction

The essence of hyperconjugation is best understood by understanding molecular orbital interaction. Here, the interaction refers to how different atomic orbitals mix to form new orbitals that belong to the whole molecule, not just individual atoms.
In hyperconjugation, the \(\sigma\) electron orbitals of a C-H bond mix with the \(\pi\)-orbital or an empty orbital of an adjacent carbon.
This mixing leads to the formation of what is known as an 'extended molecular orbital'.

• These extended orbitals are more stable because they lower the overall energy of the system.
• This interaction is a subtle but effective stabilizing factor, particularly in carbocations, where the positive charge can be delocalized over several atoms instead of being concentrated on one.