Question

Which of the following statements is not true about the resonance contributing structures of a resonance hybrid?

• A. Contributing structures contribute to the resonance hybrid in proportion of their energies.
• B. Equivalent contributing structure make the resonance very important
• C. Contributing structures represent hypothetical molecules having no real existences.
• D. Contributing structures are less stable than the resonance hybrid

Answer 1

Answer: (A)

Contributing structures contribute to the resonance hybrid in proportion of their energies.

Individual Lewis structures of a resonance hybrid are hypothetical mental constructs, and the molecular geometry and properties implied by each structure standing alone do not correspond to any real chemical species. To correctly interpret the molecular structure described by a resonance hybrid, all significant contributors of the resonance hybrid must be considered together, since the hybrid represents the actual molecule as their "average", with bond lengths and other structural parameters taking on intermediate values compared to those expected for the individual Lewis structures of the contributors, were they to exist as "real" chemical entities.
The contributing structures differ only in the formal apportionment of electrons to the atoms, and not in the actual physically and chemically significant electron or spin density. While contributing structures will differ in formal bond orders and, possibly, in formal charge assignments,the contributing structures of a resonance hybrid all represent a single chemical species. In particular, each contributing structure represents the same molecular geometry (position of atomic nuclei) and electron/spin distribution. Because electron delocalization lowers the potential energy of a system, any species represented by a resonance hybrid is more stable than any of the (hypothetical) contributing structures. The difference in potential energy between the actual species and the (computed) energy of the contributing structure with the lowest potential energy is called the resonance energy or delocalization.
conclusion; hence the option (A) is not true.