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.

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(sp(2))-H positions provide superacids as evidenced by their enthalpies of deprotonation ΔHacid(1bCN) = 257.2 and ΔHacid(2bCN) = 250.9 kcal mol(-1), which are close to the threshold of hyperacidity of 245 kcal mol(-1). On the other hand hexacyclic system 3 cyanated at all possible substitution sites along the perimeter except the acidic C(sp(3))-H position provides a true hyperacid with ΔHacid(3aCN) = 242.8 kcal mol(-1). The reason behind the dramatic acidifying effect is a vigorous anionic resonance effect in the corresponding conjugate bases assisted by a 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 Hückel's (4n + 2)π 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.