Chemical Reactivity and Quantifying the Intra- and Intermolecular Interactions in Zwitterionic Compounds

A zwitterionic Schiff base, (E)-2-((2-(1-hydroxyethyl)phenyliminio)methyl-6- methoxyphenolate (L-1) was prepared and fully characterized by spectral methods. The crystal structure was determined by using single crystal X-ray diffraction study. Inter and intra-molecular interactions in L-1 and similar zwitterionic Schiff bases (L-2=(E)-2-(((2hydroxyethyl)iminio)phenyl)methyl-5-(prop-2yn-1-yloxy)phenolate and L-3=(E)-2-(2-hydroxy-3methoxybenzylideneammonio)-3-(1H-imidazol-3-ium-4-yl) propanoate) have been established via topological analysis by considering the presence of (3,-1) bond critical points (BCP) between the interacting atoms using the approach of QTAIM (Quantum Theory of Atoms In Molecules) with the aid of ADF (Amsterdam Density Functional) 2017 package. Furthermore, Hirshfeld 2D fingerprint plots and 3D deformation densities were used to determine the interactions quantitatively. The L-1-L-3 forms a six-member pseudo cycle via an intramolecular N-HO hydrogen bond, and the crystal structure is further stabilized by the presence of stacking interactions. The effect of hydrogen bonding interactions of the molecule on infra red frequencies has been studied using DFTB (Density Functional based Tight Binding) method with ADF. The effect of intermolecular interactions of these compounds towards biomolecules was studied by using Auto Dock Vina and QTAIM analysis.