A DFT study to design super- and hyperacids with 1-(cyclopenta-2,4-dien-1-yl)-4-nitrobenzene and 3-(cyclopenta-2,4-dien-1-ylmethylene)-6-methylenecyclohexa-1,4-diene molecules

Abstract

B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) calculations reveal that 1-(cyclopenta-2,4-dien-1-yl)-4-nitrobenzene (1a) and 3-(cyclopenta-2,4-dien-1-ylmethylene)-6-methylenecyclohexa-1,4-diene compounds (3a) and their cyano derivatives (2a & 4a) exhibit moderately acidic to hyperacidic behaviour. The computed gas phase enthalpies of deprotonation ΔH_acid(2a) = 252.2 and ΔH_acid(4a) = 238.2 kcal mol⁻¹ crossed the threshold of superacidity and hyperacidity. To the best of our knowledge, this is the highest hyperacidity value obtained to date with stable small molecules.