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Weak hydrogen bonds, such as O-H···π and C-H···O, are thought to direct biochemical assembly, molecular recognition, and chemical selectivity but are seldom observed in solution. We have used neutron diffraction combined with H/D isotopic substitution to obtain a detailed spatial and orientational picture of the structure of benzene-methanol mixtures. Our analysis reveals that methanol fully solvates and surrounds each benzene molecule. The expected O-H···π interaction is highly localised and directional, with the methanol hydroxyl bond aligned normal to the aromatic plane and the hydrogen at a distance of 2.30 Å from the ring centroid. Simultaneously, the tendency of methanol to form chain and cyclic motifs in the bulk liquid is manifest in a highly templated solvation structure in the plane of the ring. 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. This demonstrates that weak hydrogen bonding can modulate existing stronger interactions to give rise to highly ordered cooperative structural motifs that persist in the liquid phase. Understanding liquid behavior is a challenge due to their disorder nature and rapid molecular rearrangements. Here, the authors show how weak interactions between OH groups and aromatic rings can participate in cooperative mechanisms that give rise to highly structured molecular arrangements in the liquid state.

Pioneer of polyamorphism and enthusiast for the solid state.

Letter to the Editor

Undergraduate practical classes that include more real science are to the benefit of students, teachers and society more broadly.

There are plenty of online resources to ensure that learning can continue for students who cannot access universities during a pandemic, but what options are there for practical aspects of science courses? Daren J. Caruana, Christoph G. Salzmann and Andrea Sella offer a manifesto for home-based experiments.

Each lab is a place where children are able to build things such as rockets, periscopes, comets or modelling-dough electrical circuits; they can make meringues or a loaf of bread and look at them under a microscope; or they can create musical instruments out of vegetables and play them. The more serious issue is how to support an inventor or scientist in residence; ideally, it should be a scientifically or technically trained person who can help to guide the ideas of the children.

The structures of equimolar mixtures of the commonly used polar aprotic solvents dimethylformamide (DMF) and dimethylacetamide (DMAc) in dimethylsulfoxide (DMSO) have been investigated via neutron diffraction augmented by extensive hydrogen/deuterium isotopic substitution. Detailed 3-dimensional structural models of these solutions have been derived from the neutron data via Empirical Potential Structure Refinement (EPSR).The intermolecular Centre-of-Mass (CoM) distributions show that the first coordination shell of the amides comprises 13-14 neighbours, of which approximately half are DMSO. In spite of this near ideal coordination shell mixing, the changes to the amide-amide structure are found to be relatively subtle when compared to the pure liquids. Analysis of specific intermolecular atom-atom correlations allows quantitative interpretation of the competition between weak interactions in solution. We find a hierarchy of formic and methyl C-H to O hydrogen bonds form the dominant local motifs, with peak positions in the range 2.5-3.0 Å. We also observe a rich variety of steric and dispersion interactions, including those involving the amide pi-backbones. This detailed insight into the structural landscape of these important liquids demonstrates the versatility of DMSO as a solvent and the unparalleled resolution of neutron diffraction, which is critical for understanding weak intermolecular interactions at the nanoscale and thereby tailoring solvent properties to specific applications.

A review of Dan Egan’s book The Devil’s Element , where he explores the element that both makes plants grow and toxifies our water — phosphorus.

Weak hydrogen bonds, such as O-H\\(\\cdots\\pi\\) and C-H\\(\\cdots\\)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 \\(\\pi\\) 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\\(\\cdots\\pi\\) 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\\(\\cdots\\pi\\) 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.