Solvation-controlled clustering of a phenol-pyridine acid-base pair

Solvent effects on acid-base interactions between phenol and pyridine have been observed via mass spectrometry of solutions containing phenol, pyridine and water, alcohol and nitrile solvents. In the solvents having sufficiently long alkyl chains to solvate phenol and pyridine, such as propan-1-ol and propionitrile, the phenol-pyridine interaction was limited to the inter-unimolecular interactions. However, in the solvents having short alkyl chains such as methanol and acetonitrile, and in water, clustering between phenol and pyridine was observed as a result of inter-cluster interactions. The phenol molecules also formed clusters in methanol and acetonitrile, but not in propan-1-ol or propionitrile. This indicates that the observed clusters are controlled by the solvation structure depending on the solvent alkyl-chain length.