Surfing the π-clouds for Non-covalent Interactions: A comparative Study of Arenes versus Alkenes

A comparative study by NMR spectroscopy using molecular balances indicates that non-covalent functional group interactions with an arene dominate over those with an alkene and a p-facial intramolecular hydrogen bond from a hydroxyl group to an arene is favoured by ~1.2 kJ mol-1. The strongest interaction observed in this study is with the cyano group and analysis of the series of Et, CH=CH2, C≡CH and C≡N groups is indicative of a weak long range electrostatic interaction and a correlation with the electrophilicity of the Ca atom of the Y substituent. Changes in the free energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β

Noncovalent Interactions of pi Systems with Sulfur: The Atomic Chameleon of Molecular Recognition

The relative strength of noncovalent interactions between a thioether sulfur atom and various π systems in designed top pan molecular balances was determined by NMR spectroscopy. Compared to its oxygen counterpart, the sulfur atom displays a remarkable ability to interact with almost equal facility over the entire range of π systems studied, with the simple alkene emerging as the most powerful partner. With the exception of the O⋅⋅⋅heteroarene interaction, all noncovalent interactions of sulfur with π systems are favoured over oxygen