AbstractDicationic 10‐C‐5 species14, formally two‐electron oxidation products of 1,8‐bis(arylthio)‐9‐(2,6‐dimethoxyaryl)‐10‐phenylanthracenes, are prepared and characterized by NMR spectroscopy. Evidence is presented for a bis‐sulfonium structure containing a hypervalent trigonal bipyramidal (TBP) carbon atom. Dicationic species14, prepared by the reaction of the appropriate diol with strong acid in liquid sulfur dioxide or sulfurylchlorofluoride, are stable for indefinite periods at room temperature in these solutions. Structural features common to these compounds which stabilize the TBP geometry sufficiently to allow their direct observation are as follows: (a) electronegative apical ligands (sulfonium sulfur atoms), (b) five‐membered rings linking each apical position to an equatorial position, (c) geometric constraints built into the tridentate ligand in a pattern designed to stabilize TBP, relative to tetrahedral carbon, (d) three relatively electropositive (sigma‐donor) equatorial ligands, which decrease the effective electronegativity of the central carbon atom of the threecenter bond, (e) a strain‐free, bidentate π‐acceptor equatorial ligand with its π‐axis parallel with the electron‐rich three‐center four‐electron bond axis, and (f) possible residual aromaticity (bis‐ipso‐aromaticity) in the equatorial six‐membered ring incorporating the hypervalent carbon atom.A low‐temperature19F NMR study of14bsets an upper limit for ΔG≠−100°Cof ca. 4 kcal/mol for a hypothetical process which would interconvert unsymmetrical species30and30′ if such a tautomeric mixture were to represent the structure of14. Evidence against such a tautomeric equilibrium is adduced from the upfield shift of 0.65 ppm observed for the proton meta to the two methoxyl substituents of dication14arelative to the comparable proton in21a, the model dication lacking one of the two arylthio substituents of14a. This is most easily explained by postulating a nucleophilic interaction of the second