Attraction or repulsion? Theoretical assessment of bulky alkyl groups by employing dispersion-corrected DFT.

London dispersion, which is the most widespread attractive part of van der Waals force, can be enhanced by introducing a bulky alkyl group to the interacting molecules. However, this strategy will also result in increased steric repulsion. Our theoretical investigation of the attraction-repulsion balance of alkyl groups is implemented, based on an intramolecular configuration torsion system, by varying the sizes and positions of alkyl groups and employing density functional theory (DFT) with or without dispersion correction. The more stabilized folded configurations, higher conversion energy barriers, and stronger alkyl-π interactions are all obtained within the dispersion-corrected DFT calculations. The position of the alkyl is the obvious controlling factor in the configuration conversion. The attractive dispersion effect of the bulky alkyl is better reflected than the steric repulsion. Furthermore, the present findings separate two different reaction pathways depending on two different stereoisomers of the unfolded reactants and the DFT+D3 simulated pathways were proved to be more reasonable.