Electronic effect of ionic‐pair substituents

Abstract

For conventional organic substituents, an almost linear relationship can be established between the para Hammett constants in aqueous solutions and chemical shifts or natural population analysis charges (NPA charges). Based on these correlations, the Hammett constants of six synthesized ionic-pair substituents were estimated via the chemical shifts, which were well in agreement with the results calculated by NPA charges. The para Hammett constants of 89 different ionic-pair substituents (77 anion-cationic and 12 cation-anionic) were therefore calculated in the gas phase based on the density functional theory method. The results show that both the anion-cationic and cation-anionic substituents are electron-withdrawing groups and the different cation-anion combinations could tune the Hammett constants of the ionic-pair substituents in a range from 0.03 to 0.77.

The relationships of catalytic activity of metal Schiff base catalysts and the Hammett constants of their anion–cationic substituents on ligand

“…We deduce that there should also be a linear relationship between the Hammett constants and the reactivity. The Hammett constants of their anion–cationic substituents on ligand were calculated via the method reported in our previous work, and the reaction barriers ( RB ) were used as the reactivity parameter. Totally 10 different anions (PF 6 − , AlCl 4 − , BF 4 − , AsF 6 − , SbF 6 − , AlF 4 − , CF 3 CO 2 − , CF 3 SO 3 − , NO 3 − , and Cl − ) were used in our previous work .…”

“… b The Hammett constant were calculated according to reference. c The multi‐atomic anions of ionic‐pair substituent in large size were chosen. TOF , turnover frequency…”

“…a The multi‐atomic anions of ionic‐pair substituent in large size were chosen. b The Hammett constant were calculated according to reference . TOF, turnover frequency…”

“…Based on the linear relationship between the para Hammett constants σ and the natural population analysis (NPA) charge q of the para carbon atom of the conventional monosubstituted benzenes ( σ = 3.762 + 18.467 q , R 2 = 0.94), the Hammett constants of ionic‐pair substituents were obtained by calculating the natural population analysis charge q of their para carbon atom at the B3LYP/6‐311++G* level in the gas phase …”

“…Because of the difficulty of the synthesis of some ionic substituted benzene, few Hammett constants σ of ionic substituents, which are important to design and improve the catalysts, can be found in literatures. Recently, we established a convenient method to predict the Hammett constants of ionic‐pair substituents . If a general relationship between the catalytic activity of metal Schiff base catalysts and the Hammett constants of their ionic‐pair substituents on ligand is built, it will be helpful and convenient to design the catalysts and tune their reactivity.…”