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

• Published in: Journal of organic chemistry 2010-11, Vol.75 (22), p.7670-7681
• Main Authors: Vianello, Robert, Maksić, Zvonimir B
• Format: Article
• Language: English
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Electrons; Exact sciences and technology; Gases - chemistry; Hydrogen-Ion Concentration; Molecular Structure; Nitriles - chemistry; Organic chemistry; Polycyclic Aromatic Hydrocarbons - chemistry; Preparations and properties; Quantum Theory
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo101581a

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 ΔH acid(1b CN ) = 257.2 and ΔH acid(2b CN ) = 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(sp3)−H position provides a true hyperacid with ΔH acid(3a CN ) = 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 pK a values in DMSO show that the polycyano derivatives are powerful superacids in solutions too.