Extremal acidity of Rees polycyanated hydrocarbons in the gas phase and DMSO – a density functional study

Abstract

It is shown by using the density functional theory (DFT) calculations that Rees tricyclic[10]annulene 1 and its benzo-annelated derivative 2, substituted by CN groups at all peripheral sp2 carbon positions, represent hyperstrong neutral superacids in the gas-phase and DMSO.

Rees polycyanated hydrocarbons and related compounds are extremely powerful Brønsted superacids in the gas-phase and DMSO—a density functional B3LYP study

“…One of the very important mechanisms, which increase acidity of neutral acids, [21][22][23][24][25][26][27]50 is the anionic resonance occurring in the conjugate bases. This is the final state effect, which should increase the electron density placed on the nitrogen atoms.…”

“…Preliminary results on compounds I and II and their polycyano derivatives were reported earlier. 50 A salient structural feature of these tricyclic compounds is the central bridging C(sp 3 )-H subunit, which brings rigidity into the systems, thus ''freezing'' the annulene network of the p-bonds formed along the molecular perimeter. It will appear that neither of three prototropic tautomers I, II and III belongs to the most stable structure, although they are minima on the potential energy hypersurface (PES).…”

Aromaticity of Rees-type hydrocarbons—a DFT computational study

“…The annulene character is lost and the number of Pauling's resonance structures is increased, underlying importance of smaller aromatic pelectron subsystems. The anionic resonance is very strong in the cyano derivative 1b -, which makes the neutral system 1b an extremely powerful organic superacid [29]. Finally, it can be concluded beyond any doubt that Rees hydrocarbon 2a is not a pseudo- [14]annulene, because the aromatic substructures involving a flanked annelated benzene ring and the intramolecular quasi-[10]annulene pattern strongly participate in the stabilization of the system.…”

“…This is compatible with the resonance effect between the CN fragments and the carbon p-network. It is particularly strong in anions (referred to as the anionic resonance effect), which considerably increases acidity of polycyano substituted Rees molecules [29].…”

“…B3LYP/6-31+G(d) computational scheme in accordance with an earlier study of the acidity of these systems[29]. For this purpose, we have made use of GAUSSIAN03 suite of programs[30].H H X X X X X X X X X X X X X X X X 1a (X = H) 1b (X = CN) 2a (X = H) 2b (X = CN) Scheme 1…”