The engineering of powerful non-ionic superacids in silico—a DFT-B3LYP study of open chain polycyanopolyenes

Abstract

The acidity of a number of all-trans polyenes, and some of their phenyl and naphthyl derivatives, was examined by the B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) method. A dramatic increase in their acidity was established upon multiple cyanation. The origin of the acidity amplification was identified as the increased stability of the resulting conjugate bases, which is mirrored in Koopmans' term appearing in the triadic analysis. It is important to emphasize that many of the studied polycyano compounds have already been synthesized. Others are probably synthesizable and their preparation is strongly recommended. Some of the examined systems come close to the acidity threshold of 245 kcal mol⁻¹ that characterizes hyperacids. The acidity of different tautomeric forms of the same organic acid is briefly discussed.