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Which set of the following statements about resonance is entirely correct? (a) Resonance is an intramolecular phenomenon. (b) Resonance involves delocalization of both sigma and pi electrons. (c) Resonance involves delocalization of pi electrons only. (d) Resonance lowers the potential energy of an acyclic molecule. (e) Resonance has no effect on a molecule's potential energy. (f) Resonance is the only way to increase molecular stability. (g) Resonance is not the only way to increase molecular stability. (h) Any resonating molecule is always more stable than any non-resonating molecule. (i) A single canonical structure explains all features of a molecule. (j) The resonance hybrid explains all features of a molecule. (k) The resonating structures are real and the hybrid is imaginary. (l) The resonance hybrid is real and the resonating structures are imaginary. (m) The resonance hybrid is always more stable than every canonical structure.

1. (a), (c), (d), (g), (j), (l), (m)
2. (a), (b), (d), (f), (i), (k)
3. (c), (e), (g), (j), (l)
4. (a), (c), (d), (g), (j), (l)

Correct answer: (a), (c), (d), (g), (j), (l), (m)

Solution

True statements: (a) intramolecular, (c) only pi/lone-pair electrons delocalize (not sigma), (d) it lowers PE/stabilizes, (g) it is not the only stabilizing factor, (j) the hybrid represents the true molecule, (l) the hybrid is real while canonical forms are imaginary, and (m) the hybrid is more stable than any single canonical structure. Statements (b), (e), (f), (h), (i), (k) are false.

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