Conformers of diheteroaryl ketones and thioketones: a quantum chemical study of their properties and fundamental intramolecular energetic effects

Abstract

The conformational behavior of ten diheteroaryl ketones and thioketones is investigated using various quantum chemical methods. These ketones and thioketones are formed by the disubstitution of formaldehyde and thioformaldehyde with such a heteroaryl group as 2-furanyl, 2-thiophenyl, 2-selenophenyl, 2-pyrrolyl or 1-methyl-2-pyrrolyl. For these compounds, their conformational preference and the energetic ordering of their conformers are determined at the MP2 and B3LYP levels of theory. Energetic barriers resulting from the interconversion between conformations are also estimated. The natural bond orbital (NBO) and interacting quantum atoms (IQA) methods are used to study fundamental intramolecular energetic effects influencing the stability of individual conformers. The results of the two methods indicate the great significance of the effect associated with electron delocalization (in the form of either NBO donor-acceptor interactions or the IQA interatomic exchange-correlation interaction energy) in governing the conformational behavior of the investigated diheteroaryl ketones and thioketones.

A Test of Various Partial Atomic Charge Models for Computations on Diheteroaryl Ketones and Thioketones

“…The tabulated values have been calculated using selected models that have operated on the molecular wave functions/electron densities computed at the B3LYP/def2-QZVPP level of theory (a complete set of results obtained from all ten models of partial atomic charge, as well as at the HF/def2-QZVPP, B3LYP/def2-QZVPP and MP2/def2-QZVPP levels of theory can be found in Tables S8-S13 in Supplementary Materials). Additionally, the relative electron energies ∆E and full-density dipole moments µ obtained from the previous regular calculations at the B3LYP/def2-QZVPP level [30,32] are also presented in Tables 1 and 2. The values of ∆E allow us to establish the reference orderings of conformers for 1a-5a and 1b-5b.…”

“…The molecular structures of 1a-5a and 1b-5b are taken from our previous works [30][31][32] in which Becke's three-parameter hybrid exchange functional combined with the correlation functional of Lee, Yang and Parr (B3LYP) [33][34][35] and the def2-QZVPP basis set [36] were used to optimize the geometries of the isolated molecules of 1a-5a and 1b-5b. It was also established there that for each of the compounds its three conformations could be formed by the rotation of heteroaryl substituents about the single C-C bonds linking these substituents with the C atom of carbonyl/thiocarbonyl group.…”

“…Such a procedure taking only E elst into consideration assumes that the electrostatic effects play an important role in governing the conformational behavior of investigated compounds. These effects, indeed, contribute significantly to the ordering of conformers for diheteroaryl ketones and thioketones [30,32].…”

The ANANKE relative energy gradient (REG) method to automate IQA analysis over configurational change

“…This is a robust topological energy partitioning method that disentangles the total energy of a system into intra-and interatomic contributions of various types. IQA is inspired by earlier work [23] and has been used by several groups to study a wide variety of interactions and phenomena, including but not limited to: halogen-halogen interactions in perhalogenated ethanes [24], halogen bond formation [25], conformational analysis of diheteroaryl ketones and thioketones [26], proton transfer reactions [27], formation of an intramolecular bond path between two electronegative atoms [28], substituent effects in electronically excited states [29], cooperative and anti-cooperative effects in resonance-assisted hydrogen bonds in malondialdehyde [30], short-range electrostatics in torsional potentials [31], new insights in atomatom interactions for future drug design [32], the anomeric effect in halogenated methanols [33], hydrogen-hydrogen interaction in planar biphenyl [34], the steric repulsion in congested molecules [35], charged hydrogen-bonded complexes [36], trapping of CO 2 by adduct formation [37], and the diastereoselective allylation of aldehydes [38].…”

The effects of higher orders of perturbation theory on the correlation energy of atoms and bonds in molecules

“…However, when correlation energy is combined with exchange energy, as was recently made possible [17] in DFT, then it is calculated in a growing number of studies, due to DFT's reduced computational cost. In the last few years a surge of papers appeared using IQA and offering chemical insight into a wide variety of phenomena, such as halogen-halogen interactions in perhalogenated ethanes, [18] conformations in diheteroaryl ketones and thioketones, [19] substituent effects in electronically excited states, [20] cooperative and anti-cooperative effects in resonance-assisted hydrogen bonds in malondialdehyde, [21] the hydrogen-hydrogen interaction in planar biphenyl, [22] steric repulsion in congested molecules, [23] and the diastereoselective allylation of aldehydes. [24] None of the aforementioned work reports atomically partitioned correlation energy by itself (i.e., isolated from exchange) but the current article does, and obtains it from MP2, MP3, and MP4SDQ wave functions.…”