A density functional theory study on the superacidity of sulfuric, fluorosulfuric, and triflic acid derivatives with two cyclopentadiene rings: ion pairs formation in the gas phase

The gas phase acidity of organosulfuric acid derivatives with two cyclopentadiene rings replacing the doubly‐bonded oxygen atoms was computationally assessed using the B3LYP DFT functional and 6–311++G(d,p) basis set. Introduced five‐membered rings increased the acidity through the delocalization of the excess negative charge in conjugates bases and by providing positions to accommodate electron withdrawing substituents such as F and CN. The calculated enthalpies of deprotonation (∆ H acid ) of polycyanated systems were as low as 227.8 to 263.2 kcal mol –1 indicating exceptional superacidity. Substitution of one OH moiety by F or CF 3 groups offered additional acidifying effect by preventing prototropic tautomerism in the neutral acids that acts towards lowering the acidity. The designed systems spontaneously protonated H 2 O and NH 3 in the gas phase and produced stable ion pair clusters.