2022/12/20 by Camilla Di Mino, Andrew G. Seel, Di Mino, Camilla +13
Chemistry · Physics and Astronomy · #Chemical Physics (physics.chem-ph) #Crystallography and molecular interactions #FOS: Physical sciences #Molecular spectroscopy and chirality #Soft Condensed Matter (cond-mat.soft) #Spectroscopy and Quantum Chemical Studies
paper · pdf · doi:10.48550/arxiv.2212.10266
openalex publication_date 2022/12/20 · openalex created_date 2023/01/04 · openalex updated_date 2026/07/28
Weak hydrogen bonds, such as O-H⋯π and C-H⋯O, are pivotal in a wide range of important natural and industrial processes including biochemical assembly, molecular recognition, and chemical selectivity. In this study we use neutron diffraction in conjunction with comprehensive H/D isotopic substitution to obtain a detailed spatial and orientational picture of the structure in benzene-methanol solution. This system provides us with a prototypical situation where the aromatic ring can act as an hydrogen bond acceptor (via the π electron density) and/or a hydrogen bond donor (via the CH groups), with the potential for cooperative effects. Our analysis places benzene at the centre of our frame-of-reference, and reveals for the first time that in solution the O-H⋯π interaction is highly localised and directional, the hydrogen atom being located directly above/below the ring centroid at a distance of 2.30 Å and with the hydroxyl bond axis normal to the aromatic plane. The tendency of methanol to form chain and cyclic motifs in the bulk liquid is manifest in a highly templated, symmetrical equatorial solvation structure; the methanol molecules surround the benzene so that the O-H bonds are coplanar with the aromatic ring while the oxygens interact with C-H groups through simultaneous bifurcated hydrogen bonds. By contrast, C-H⋯π interactions are relegated to the role of more distant spectators. The experimentally observed solvation therefore demonstrates that weak hydrogen bonding can give rise to strongly-ordered cooperative structural motifs also in the liquid phase.