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Problems: Resonance

Problem : Which of the following pairs are resonance structure? For pairs that are resonance structures, use the curved-arrow formalism to derive the second structure from the first.

Figure %: Problem 1

Only (a) is a pair of resonance structures.

Problem : One of the resonance structures of phenanthrene, a hydrocarbon found naturally in coal tar, is shown below. It turns out that this is only one of five resonance structures that can be drawn for this compound.

(a) Using the curved-arrow formalism to aid you, find the other four resonance structures of phenanthrene (fill in the incomplete structures).

Figure %: Problem 2
(b) Assuming that each resonance structure contributes equally to the final resonance hybrid of phenanthrene, identify the longest bond and shortest bond in phenanthrene and give their respective bond orders.

Figure %: Solution