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Fulvene versus Benzene

Failures, as are successes, are an integral part of a structure elucidator’s role. What differentiates a good elucidator from a bad one is the capability of an elucidator to learn from his/her failures. The most common obstacle that can hold a structure elucidation process from becoming a success is structural bias. (This is based on my experiences with elucidators worldwide.)

A good stance to best avoid structural bias is to be aware of different alternative structures especially those not commonly encountered during a routine structure elucidation. Below is a case in point. The unknown is comprised of two fragments such that the hybridization states of all the carbons are sp2 and the ring size is restricted to 5 or 6. For clarity reasons, the carbon atoms in red are the ones to be arranged.


Two candidate structures are shown below. A common structural bias is to take the 6 sp2 carbons and complete a benzene ring (right structure). The alternative structure is work out a fulvene group (left structure). References are included for both structures.