The most public demonstration of the power of Pauling's resonance ideas came when he used them to solve one of the oldest
problems in organic chemistry.
Benzene was a mystery. It was known to be composed of six carbon atoms and six hydrogen atoms, but the structure of the benzene
molecule had eluded definitive analysis. In the winter of 1932-33, Pauling and a graduate student, George Wheland, set out
to solve the structure according to Pauling’s concept of resonance.
By spring they finished a paper, "The Nature of the Chemical Bond V. The quantum-mechanical calculation of the resonance energy
of benzene and naphthalene and the hydrocarbon free radicals," in which benzene was described as resonating between five extreme,
or "canonical," structures. "The properties of the molecule," Pauling wrote, "would then be expected to be a sort of average
of the properties of the individual molecules."
Pauling and Wheland's approach seemed to work: The values calculated from their resonating structure fit what was known about
the molecule's structure, reactivity, and stability. They expanded their approach to other aromatic molecules like naphthalene
(using no fewer than forty-two canonical structures) and to hydrocarbon free radicals.