organic chemistry - Is pyrene aromatic despite failing Hückel's rule?

Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic.

Considerations:

1. Pyrene is cyclic. ✓


2. Pyrene is flat (planar). ✓


3. Pyrene has 16 π electrons.


4. Every atom in the ring structure of pyrene is $\ce{sp^2}$ hybridized. ✓

The problem is that pyrene fails the $4n+2$ rule. $4n + 2 \neq 16$ where $n$ is an integer.

Something leads me to suspect that Hückel's rule is an oversimplification here. Or is pyrene indeed non-aromatic?

Answer

Pyrene is aromatic. The Hückel $4n+2$ rule works best with monocyclic ring systems. If you look at the following resonance structure for pyrene with a central double bond, the monocyclic periphery has 14 π electrons (ignoring the greyed-out central double bond), but that is a rationalization.

Nonetheless, pyrene undergoes reactions characteristic of aromatic systems and has ring currents expected from aromatic systems.