13C NMR and ab Initio/IGLO Study of Protonated Oxocarbons: Poly-O-protonated Squaric, Croconic, and Rhodizonic Acids and Their Aromatic Nature. Preparation and Study of Tetrahydroxy- and Diaminodihydroxyethene Dications

Abstract

The protonation of oxocarbons in superacidic solutions has been studied. Squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione, 2), croconic acid (4,5-dihydroxy-4-cyclopentene-1,2,3-trione, 2), and crodizonic acid (5,6-dihydroxy-5-cyclohexene-1,2,3,4-tetraone, 4) were poly-O-protonated with Magic Acid (1:1 SbF 5 +FSO 3 H) or fluorosulfuric acid at low temperatures and characterized by 13 C NMR spectroscopy. The protonation of oxalic acid and oxamide has also been studied in HSO 3 F/SbF 5 /SO 2 solution at -78 o C and the resulting ethene dications were characterized by 13 C NMR spectroscopy