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Polycyano Derivatives of some Organic Tri- and Hexacyclic Molecules are Powerful Super- and Hyperacids in the Gas-Phase and DMSO - Computational Study by DFT Approach

The B3LYP/6-311+G(2df, p)//B3LYP/6-31+G(d) calculations convincingly show that tricyclic organic compounds 1 and 2 offer scaffolds suitable for tailoring powerful neutral organic acids. Their cyanation at all C(sp2)-H positions provide superacids as evidenced by their enthalpies of deprotonation ΔHacid(1bCN) = 257.2 and ΔHacid(2bCN) = 250.9 kcal/mol, which are close to the threshold of hyperacidity of 245 kcal/mol. On the other hand hexacyclic system 3 cyanated at all possible substitution sites along the perimeter except the acidic C(sp3)-H position provides a true hyperacid with ΔHacid(3aCN) = 242.8 kcal/mol. The reason behind dramatic acidifying effect is vigorous anionic resonance effect in the corresponding conjugate bases assisted by cooperative substituent effect of the CN groups. It is convincingly shown that compounds 1 and 2 represent rigid antiaromatic quasi-[12]annulene and aromatic quasi-[14]annulene par excellence, respectively, conforming to Huckel's (4n + 2)pi electron count rule in the bridged polycyclic systems. Calculations of the pKa values in DMSO show that the polycyano derivatives are powerful superacids in solutions too.

gas–phase acidity; superacidity; hyperacidity; annulenes; polycyano hydrocarbons

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