theory of resonance
in chemistry, theory by which the actual normal state of a molecule is represented not by a single valence-bond structure but by a combination of several alternative distinct structures. The molecule is then said to resonate among the several valence-bond structures or to have a structure that is a resonance hybrid of these structures. The energy calculated for a resonance hybrid is lower than the energies of any of the alternative structures; the molecule is then said to be stabilized by resonance. The difference between the energies of any one of the alternative structures and the energy of the resonance hybrid is designated resonance energy.
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