Intramolecular resonance assisted N–H⋅⋅⋅O=C hydrogen bond and weak noncovalent interactions in two asymmetrically substituted geminal amido-esters: Crystal structures and quantum chemical exploration

Abstract

Two asymmetrically substituted geminal amido-esters, namely ethyl (2E)-2-[(2,5-dimethoxy phenyl)carbamoyl]-3-[(4-nitrophenyl)amino] prop-2-enoate (I) and ethyl (2E)-2-[(9,10-dioxo-9,10-dihydroanthracen-1-yl)carbamoyl]-3-(phenylamino) prop-2-enoate (II) were synthesized and the nature and strength of intramolecular resonance assisted hydrogen bond (RAHB) and non-RAHB was studied. X-ray analysis revealed that intramolecular N–H⋅⋅⋅O, and C–H⋅⋅⋅O interactions lead to the formation of angularly fused pseudo tricyclic (A-C) motif in compound I and fused pseudo pentacyclic (A-E) motif in compound II. Intramolecular RAHB; non-RAHB interactions are characterized and quantified by Bader's quantum theory of atoms-in-molecules approach (QTAIM). In both compounds, ring A was found to exhibit intramolecular RAHB characteristics. Crystal structures of I and II are stabilized by weak intermolecular C–H⋅⋅⋅O, C–H⋅⋅⋅π, and π⋅⋅⋅π interactions. Intermolecular interaction energies for different molecular dimers in I and II have been quantified by using the PIXEL, QTAIM, and DFT methods. The pseudoring stacking interaction is observed only in compound II whereas no such stacking interactions are seen in compound I. Hirshfeld surface (HS) analysis suggested that the H⋅⋅⋅H and O⋅⋅⋅H contacts are the first and second dominant contacts in both crystal structures. The theoretical charge density analysis revealed that the C–H⋅⋅⋅O and C–H⋅⋅⋅C(π) interactions produce closed-shell characteristics. Further, the crystal packing of compounds I and II analyzed based on the energy frameworks.