How many electrons in benzene (C₆H₆) form the delocalized π-electron cloud?

Benzene (C₆H₆) is a planar cyclic hydrocarbon consisting of six carbon atoms arranged in a hexagonal ring. Each carbon atom in benzene is sp² hybridized. This means that every carbon forms three sigma (σ) bonds—two with adjacent carbon atoms and one with a hydrogen atom. The remaining unhybridized p-orbital on each carbon atom is perpendicular to the plane of the ring.

These six p-orbitals overlap sideways with each other, forming a continuous π-electron cloud above and below the ring. Each carbon atom contributes one electron from its p-orbital, resulting in a total of six delocalized π-electrons. These electrons are not localized between specific carbon atoms; instead, they are shared equally across the entire ring.

This delocalization of electrons provides extra stability to benzene, a phenomenon known as aromatic stabilization or resonance energy. The delocalized π-electron system satisfies Hückel’s rule (4n + 2 = 6, where n = 1), confirming benzene’s aromatic nature.

The six delocalized π-electrons create a ring current, which is responsible for the chemical and magnetic properties of aromatic compounds. This structure was first proposed by Kekulé and later confirmed through quantum mechanical models and X-ray diffraction studies.

In contrast, compounds that do not have delocalized π-electrons show different reactivity and lack aromatic stability. The concept of π-electron delocalization is central to understanding the behavior of aromatic compounds in organic chemistry, including substitution reactions like nitration, halogenation, and Friedel–Crafts reactions.

Therefore, benzene has six delocalized π-electrons, forming a stable aromatic ring system that is symmetrical and energetically favored.