Illustrated Glossary of Organic Chemistry

Resonance hybrid: A weighted average of all significant resonance contributors depicting the true electronic structure of a molecule.

Resonance contributors for acetate ion. The first two contributors have no resonance contributor preference rule violations, so these are significant resonance contributors and are included when constructing the resonance hybrid. The third contributor violates three resonance contributor preference rules, so this contributor is not significant, and is not considered when constructing the hybrid.

Resonance hybrid for acetate ion.