Conformational analysis of chalcone 1-(4-nitrophenyl)-2-propen-3-(4-hydroxy-3-methoxyphenyl)-1-one

Chalcones can be classified as α,β-unsaturaded ketones. They have been focus of attention due to the rich variety of biological activities they present as a function of their different substituents. Aiming to better understand and describe such structures, this work proposes the conformational analysis of chalcone represented in Figure 1 below. Theoretical calculations were employed to both determine the structures involved in the equilibrium and understand the stereoelectronic effects involved. The chalcone was submitted to theoretical calculations using the GAUSSIAN 09 program and NBO 5.9 module for the calculations involving the natural bonding orbital theory. First, a selection of the most stable conformers was carried out through potential energy surface calculations as a function of the dihedral angles a, b and c (Figure 1) employing the HF/6-31G level of theory. From the six minimum energy points found, optimization and frequency calculations at M06-2X/6-311++G (2d, 2p) obtaining four different conformations. Two conformers with carbonyl and double bond s-cis oriented, and another two conformers in s-trans. From this data, NBO calculations were carried out at the same level of theory of the optimizations to verify the influence of the hyperconjugative effect in the conformers stabilization. The interactions involving the ligand and anti-ligand orbitals were evaluated (Table 1). Both s-cis conformations were more stable due to the planarity of the structure, which favored orbital interactions of the type →showing that this effect contributes more effectively to the stabilization of these structures.