Molecular structure, proton affinity and hydrogen bonds of (2-hydroxyethyl)amine- N -oxides: DFT, MP2 and FTIR study

Ion Pair Structures and Hydrogen Bonding in RnNH4-n Alkylammonium Ionic Liquids with Hydrogen Sulfate and Mesylate Anions by DFT Computations

Density function theory calculations are employed to study the interaction of amines bearing different numbers of alkyl substituents of different sizes on the nitrogen atom with sulfuric and methanesulfonic acids. The proton affinities of the studied amines are calculated, and it is shown that the higher the value is, the more probable is its protonation. The most stable structures of the ion pairs resulting from the acid-base interaction are obtained and characterized. The geometric parameters of the ion pairs and the characteristics derived from the NBO and QTAIM analysis show that there are hydrogen bonding interactions between the cation and the anion. The hydrogen bonding character of the ion pairs and the strength of the interaction between the ions strongly depend on the nature of the cation itself. The interaction between the ions in the ion pairs weakens with the increase in the cation size. The trend of change in the structural parameters of the H-bonds and energetic characteristics in the cation series for the studied ion pairs is not dependent on the nature of the anion.

Quantum Chemical Modeling of the Structure and H Bonding in Triethanolammonium-Based Protic Ionic Liquids with Sulfonic Acids

The results of electronic structure calculations based on density functional theory (DFT) for protic ionic liquids (PILs) consisting of triethanolammonium cation paired with anion of different sulfonic acids are reported. The influence of the anion nature on the structure and interactions in the ion pairs that are formed in these PILs is discussed in detail. Multiple H-bonding interactions exist between the protons in the NH/OH groups of the cation and different oxygen atoms of the acid anion in the ion pairs. The quantum theory of "atoms in molecules" has been used to estimate the individual contributions of each hydrogen bond to the stability of the ion pair. The hydrogen-bonding interactions in the ion pairs vary in their strength ranging from weak to moderately strong. In addition to these hydrogen bonds, there are other dispersion and electrostatic-dominant interactions that play an important role in the overall stability of PILs and their physicochemical properties. Aided by results from our previous DFT studies of triethanolammonium class of PILs with inorganic anions, these new data allow us to gain an improved understanding of the structure-property relationships in the studied ionic liquids. Close to linear correlation, in particular, has been found between the melting points and the binding energies of the cation and anion in the ion pairs.