Weak hydrogen bonding as the driver of aromatic hydration
- Camilla Di Mino
- Daniel Bowron
- Michael A. Wilkinson
- Tristan G. Youngs
- Thomas F. Headen
- Andrea Sella
- Neal T. Skipper
2026-08-11
Intermolecular forces are the fundamental architects of supramolecular structure, where subtle interplays of charge distribution, entropy, and sterics determine the outcome. In aromatic molecules, the distribution of delocalised π electrons is modulated by the substituents, affecting their intermolecular interactions and introducing “holes” in the π orbitals. While increasingly well-understood in the solid state, the influence of π -holes on solvation and miscibility in the liquid remains unknown. Here, total neutron scattering and modelling-based refinement reveal the solvation of phenol, aniline, and p-nitrophenol in water. The in-plane solvation is dominated by strong classical hydrogen bonds between water and the substituents. Out of the ring plane, perpendicular OH··· π weak hydrogen bonds between water and phenol or aniline are cooperative and modulated by differences in electron density. By contrast, in p-nitrophenol, the presence of the electron-withdrawing nitro group enhances the overall molecular dipole, and introduces a pronounced π -hole that significantly disrupts the overall out-of-plane solvation. The latter is dominated by close water-O···N contacts at ≈ 3.35 Å resulting from localized charge depletion accompanied by O··· π * motifs (≈ 3.96 Å). These interactions template the structure of the surrounding water, redefining the solubility of these aromatics in water and underscoring the complex solvation of organic molecules.