The two formulae had been proposed in the last century by Kekulé. One of the amusing points, politically amusing points of it was that this chemical theory had been refuted, forbidden, by the leadership in the for- Soviet Union. They referred to a Russian paper of the last century saying a molecule is a molecule is a molecule, it has one formula. To get two formulae for one molecule is nonsense. The Kekulé idea, on the other hand, in the United States, was taken up by one good chemist who actually is the one person I know of, perhaps there are others, who got two Nobel Prizes, one for chemistry, one for politics. And with one I agree more than with the other. And the work on chemistry includes his explanation of the simultaneous existence of two formulae for the same molecule. Linus Pauling has understood, at an early state, quantum mechanics. And he said- Yes, the configuration of the electron wave functions can correspond to one Kekulé formula or the other Kekulé formula. One then can get a lower energy state by describing the wave function of the molecule as a sum of these two wave functions, corresponding to the two Kekulé formulae. Sounded plausible, was accepted.