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Breaking with convention: In the textbook aromatic annulenes the p orbitals are oriented perpendicular to the ring plane. In trannulenes the p orbitals form a cyclic, conjugated π system within the ring plane (see scheme). This concept of “in-plane” aromaticity was first recognized in 1979, and now representative compounds have been synthesized. The all-trans configuration of the annulene ring is stabilized by a fullerene framework, and the novel physicochemical properties of trannulenes open new opportunities for the design of light-harvesting compounds.
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Glenn A. Burley (2005) studied this question.
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