Intramolecular C–H···H–C Contacts in Diheteroaryl Ketones and Thioketones: A Theoretical Analysis

Abstract

Abstract Intramolecular C–H···H–C contacts in a set of 10 molecules, being formaldehyde and thioformaldehyde disubstituted with such a heteroaryl group as 2-furanyl, 2-thiophenyl, 2-selenophenyl, 2-pyrrolyl, or 1-methyl-2-pyrrolyl, have been studied using density functional theory (DFT), natural bond orbital (NBO) analysis, quantum theory of atoms in molecules (QTAIM), noncovalent interactions (NCI) index, and interacting quantum atoms (IQA) theory. The results illustrate the fundamental difference in perceiving these contacts from a perspective based on QTAIM-defined atomic basins against the localized-orbital perspective of the NBO theory. The presence of the C–H···H–C contacts locally destabilizes the investigated molecules, although their characterization narrowed only to the interaction between the QTAIM basins of the H atoms in the contacts shows a very weak attraction between these atoms. We demonstrate some relationships between the results obtained from different theoretical methods in order to emphasize possible similarities in their pictures of the contacts. The indication of such similarities may be important for the interpretation of theoretical results in future studies utilizing the aforementioned methods to investigate C–H···H–C contacts in various molecules.