Vibrational dynamics of the acid-alcohol hinge

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Organic alcohols and acids are very well characterized, in particular with respect to their pairing tendency. The former undergo medium strength, well characterized hydrogen bonding, whereas the hydrogen bonds between carboxylic acids are significantly stronger and the vibrational dynamics of the acidic protons becomes irregular. An obvious strategy to cope with the complex acid dimer dynamics is to study the mixed pairing of an alcohol with an acid molecule. Surprisingly, such neutral molecular pairs have remained largely uncharacterized and a recently published microwave study speculatively blames spontaneous, quantitative chemical reaction of the non-covalent pairs to esters for their elusiveness. In preliminary work, we were able to partially revise this interpretation and now want to carfully and comprehensively characterize such novel, mixed molecular pairs by Raman and infrared spectroscopy in supersonic jet expansions. This will involve chemical and isotopic substitution experiments. The hinge-like alcohol-acid complexes allow for flexible interactions at long distance between the substituents on the alcohol and carboxyl groups via subtle intermolecular forces, including chirality recognition. In the end, a new model system for the interplay of strong hydrogen bonds with weak interactions between alcoholic and acidic residues shall be enabled for the experimental benchmarking of quantum chemical and nuclear dynamical methods.