The transition states of thermally allowed pericyclic reactions are aromatic. They not only have highly delocalized structures and large resonance stabilizations (energies of concert), but also strongly enhanced magnetic susceptibilities (Λ) and appreciable NICS (nucleus-independent chemical shifts) values arising from the diatropic ring currents. Aromaticity is the consequence of cyclic electron delocalization, which can have σ and hybrid, and not just π character.
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Jiao et al. (1998) studied this question.
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