Observation of Distinct Carboxylic Acid Conformers in Aqueous Solution

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DOI http://dx.doi.org/10.1021/acs.jpclett.9b00915
Reference G. Giubertoni, O.O. Sofronov and H.J. Bakker, Observation of Distinct Carboxylic Acid Conformers in Aqueous Solution, J. Phys. Chem. Lett. `10, 3217-3222 (2019)
Group Ultrafast Spectroscopy

We investigate the molecular geometry of the carboxyl group of formic acid in acetonitrile and aqueous solutions at room temperature with two-dimensional infrared spectroscopy (2D-IR). We found that the carboxyl group adopts two distinct configurations: a configuration in which the carbonyl group is oriented anti-parallel to the hydroxyl (anti-conformer), and a configuration in which the carbonyl group is oriented at an angle of ~60° with respect to the hydroxyl (syn-conformer). These results constitute the first experimental evidence that carboxyl groups exist as two distinct and long-living conformational isomers in aqueous solution at room temperature.