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Benzocyclobutadiene warrants particular interest owing to its intermediate position between cyclobutadiene and biphenylene. X-Ray structure analysis of the stable hexaalkyl derivative (1) showed the molecular skeleton to be planar and the ground state to be best described by the resonance structures (1 A) and (1 B); (1 B) has greater weight than (1 A).
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Winter et al. (1978) studied this question.
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