Hückel’s Rule

• Hückel's rule is a criterion used to determine if a molecule is aromatic.

• Aromatic compounds exhibit unusual stability and unique properties due to the delocalization of π electrons in a conjugated ring system.

Here are the key points:

1. Cyclic Structure: The molecule must have a ring structure.

2. Planarity: The molecule must be planar, which allows for effective overlap of p orbitals.

3. Conjugated System: The molecule must have a conjugated system with alternating single and double bonds.

4. π Electrons: The molecule must have a specific number of π electrons, calculated using the formula 4n+2, where n is a non-negative integer (0, 1, 2, ...).

For example, benzene (C₆H₆):

benzene (C₆H₆)

• Cyclic Structure: Benzene has a ring structure.

• Planarity: Benzene is planar.

• Conjugated System: Benzene has alternating single and double bonds, forming a conjugated system.

• π Electrons: Benzene has 6 π electrons (one from each carbon).

Applying Hückel’s rule:

• 4n + 2 = 6

• Solving for n:

  

• Since n = 1 is a non-negative integer, benzene satisfies Hückel's rule and is aromatic.

• This explains benzene's stability and unique properties.