Using Huckel’s rule, prove that Naphthalene is aromatic.

Hückel's rule is a criterion used to determine whether a planar, cyclic molecule is aromatic based on the number of π (pi) electrons it possesses. According to Hückel's rule:

The molecule must be planar.
The molecule must be cyclic.
The molecule must have a continuous ring of p-orbitals.
The number of π electrons in the cyclic system must be 4n + 2, where n is a non-negative integer (i.e., 0, 1, 2, 3, ...).
Let's apply Hückel's rule to naphthalene, a commonly known aromatic compound:

Planarity: Naphthalene is a flat, planar molecule. It consists of two fused benzene rings, which are themselves planar.

Cyclic: Naphthalene is a cyclic compound, as it forms a closed loop.

Continuous ring of p-orbitals: In the case of naphthalene, each carbon atom in the benzene rings is sp2 hybridized, which means it has a p-orbital perpendicular to the ring plane. These p-orbitals overlap to form a continuous ring of p-orbitals, making it possible for π electrons to move freely in the π system.

Counting π electrons: Now, let's count the π electrons in naphthalene. Each benzene ring contributes 6 π electrons (3 double bonds), so two benzene rings contribute a total of 12 π electrons.

According to Hückel's rule, the number of π electrons in an aromatic system should be 4n + 2. In this case, n = 2, so:

4n + 2 = 4(2) + 2 = 8 + 2 = 10

The number of π electrons in naphthalene is 12, which doesn't satisfy 4n + 2 when n is 2. However, this doesn't necessarily mean that naphthalene is not aromatic. Naphthalene is actually an example of an aromatic compound that doesn't strictly follow Hückel's rule for 4n + 2 electrons. In such cases, it's considered to be "antiaromatic."

Antiaromatic compounds are cyclic, planar molecules with a continuous ring of p-orbitals, but they have 4n π electrons, where n is an integer. These compounds are less stable and less common than aromatic compounds.

So, in summary, naphthalene does not strictly follow Hückel's rule for aromaticity (4n + 2 electrons), but it is still considered aromatic due to its stability, which results from the delocalization of its π electrons.