resonance structure

In chemistry, resonance theory explains that a molecule's actual structure isn't represented by a single valence-bond arrangement but by a combination of several distinct, alternative structures. These are called resonance structures, and the molecule is said to resonate among them, existing as a resonance hybrid. This hybrid structure has lower energy than any of the individual alternative structures, a phenomenon known as resonance stabilization.1

A classic example is benzene, where resonance explains why all six carbon-carbon bonds are equivalent, despite initial models suggesting alternating single and double bonds. The theory, further developed by scientists like Linus Pauling, uses quantum mechanics to predict that the resonance hybrid's energy is lower than any single contributing structure. This concept applies to molecules where a single, satisfactory structure cannot be assigned using only single, double, and triple bonds.1