Strong Acidity of Some Polycyclic Aromatic Compounds Annulated to a Cyclopentadiene Moiety and Their Cyano Derivatives – A Density Functional B3LYP Study

Abstract

The acidity of the parent 1H‐benz[f]indene (1a), 1H‐benz[e]indene (2a), 1H‐benz[fg]acenaphthylene (3a) and 1H‐cyclopenta[l]phenanthrene (4a) and of their polycyano derivatives is examined in the gas phase and in DMSO by the DFT‐B3LYP methods. It is shown that the parent hydrocarbons exhibit modest acidities, whereas a dramatic increase in acidity is observed upon multiple cyanation leading to hyperstrong neutral organic superacids. It is found that polycyano derivatives undergo prototropic tautomerism with a consequence that the most stable tautomer contains a ketene imine C=C=NH functionality. The origin of their highly pronounced acidity is identified as a very strong anionic resonance effect efficiently assisted by a large number of CN groups in a concerted manner. It is stressed that the polycyanated anions are very stable and have a highly dispersed negative charge, which should lead to a low nucleophilicity and weak coordinating properties, thus making them potentially very useful in academic research and technological applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Brønsted Acidity and the Medium: Fundamentals with a Focus on Ionic Liquids

“…2.5 [93] 10.75 [2] 0.65 [94] 5.46 [98] 4.9 [96] --CF 3 CO 2 H 1352.1 [c] 3.51 [99] 12.65 [2] 0.00 [90] ----H 2 SO 4 1295 [20] 1.99 [100] 7.29 [101] À9 [33] -1.62 [102] 3.1 [80] HOTf 1278 [33] 0.3 [1] /f.d.…”

Superacidity of P(OH)3 and SO(OH)2 derivatives of cyclopentadiene and vinylcyclopentadiene in the gas phase: A computational DFT analysis

“…Cyclopentadiene has been used in designing a wide range of neutral organic acids . After deprotonation, the excess negative charge is delocalized over all atoms in the five‐membered ring followed by the formation of a 6 π‐electrons aromatic cyclopentadienyl fragment, C 5 H 5 − .…”

First principles calculations of pKa values of amines in aqueous solution: Application to neurotransmitters

“…A huge amount of chemical compounds behave as Brønsted acids (or bases) in aqueous solution, and their acidity is commonly expressed as p K a . Even though there are several experimental techniques that have been successfully applied to accurately obtain p K a 's, sometimes this becomes a challenging, or very expensive, task1, 2 Therefore it is not surprising that a large amount of effort has been devoted in the last decades to obtain reliable p K a values using theoretical methods 3–27…”