Quantification of the Strength of π-Noncovalent Interactions in Molecular Balances using Density Functional Methods

Different molecular balances were designed previously to compare noncovalent interactions. However, some balances are difficult to synthesise and there is a need for developing a computational approach. In this work, we probe noncovalent interactions of pi systems using DFT methods to assess their reliability in reproducing experimentally measured conformer populations. Based on our results, the PW6B95D3 functional performed best, followed by M11L and omega B97XD. Additionally, the simulation of the rotation of the hydroxyl group revealed stabilising OH center dot center dot center dot Alkyne and OH center dot center dot center dot Nitrile interactions that are difficult to identify experimentally. These methods were then applied to compare the strengths of sulfur center dot center dot center dot pi interactions in molecules which have not been explored experimentally. Compared to the hydroxyl counterpart, the simulation of the thiol group rotation showed that the geometry of the conformer with the two sulfur lone pairs oriented towards the aromatic ring or the double bond is stabilised, suggesting that S(LP)center dot center dot center dot pi interactions can be attractive in nature. The ability of sulfur to rearrange its electronic surrounding to form an attractive interaction with pi systems, including those with either electron-donating or withdrawing groups, was also confirmed. Overall, the results show a promising future for both qualitative and quantitative assessments of the strengths of noncovalent interactions using selected DFT techniques.