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The molecule (C═C)TTP (TTP = tetra-p-tolylporphyrin) and the triflate salt of its dication, [(C═C)TTP][OTf](2), have been synthesized and characterized. NMR spectroscopy, nucleus-independent chemical shift calculations, and the crystal structure of (C═C)TTP indicate that (C═C)TTP is antiaromatic and (C═C)TTP(2+) is aromatic.
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Thomas P. Vaid (2011) studied this question.
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