Raman spectroscopic and computational study of normal and deuterated tautomeric O-HO hydrogen bonds
Two O-H×××O hydrogen bonds together with carboxyl groups generatea closed cycle which results in appearance of proton tautomerism - formation of two identical potential walls and coordinated transferring of protons from one minimum to another (further: t-bond). An example of most regular in structural sense t-bond is a crystal of terephtalic acid (TPA) where molecules of TPA form an infinitive chains due to t-bonds. At cooling down the crystalline vibrations are ‘frozen out’ and the t-bond becomes shorter. It causes a reducing of the jumping rate and an increasing of the tunneling probability. Onset temperatures of both tunneling and ordering (termination of the hopping) processes were determined in our previous work (Pritchina E.A., Kolesov B.A. Raman spectra of terephthalic acid crystals in the temperature range 5 K–300 K. SpectrochimicaActa Part A: Molecular and Biomolecular Spectroscopy 202 (2018) 319–323).