Intramolecular nonbonding interactions in organoseleniums: Quantification using a computational thermochemical approach

Intramolecular Se⋯O nonbonding interactions in a series of ortho-formylarylselenides (O⋯Se-Y, with Y = -Me, -Ph, -CN, -Cl, and -F) are quantified using density functional theory. Two methods based on the relative stabilities of various conformers are employed in evaluating the strength of intramolecular interactions. These methods, namely, cis-trans (CT) and thermodynamic cycle (TDC), depends on the energy changes associated with conformational interconversion, where the nonbonding interaction is turned on or off (respectively, in cis and trans conformer). The strength of interactions are found to be dependent on the nature of Se-Y acceptor orbitals and follows the order Me ∼ Ph < CN < Cl < F. Natural Bond Orbital (NBO) analysis using DFT methods points to nO→σSe-Y∗ electron delocalization as the key contributing factor towards Se⋯O nonbonding interaction. Examination of the topological properties of the electron density with the Atoms-in-Molecule (AIM) method reveals that the electron density at the Se⋯O bond critical point exhibits a fairly good correlation with the nonbonding interaction energies estimated using the CT and TDC methods.