Polarized IR spectra of2-furanacetic acidand of2-furanacrylic acidcrystals were measured at 293 K and 77 K in thevO−HandvO−Hband frequency ranges. The corresponding spectra of the two individual systems strongly differ, one from the other, by the corresponding band shapes as well as by the temperature effect characterizing the bands. The crystal spectral properties remain in a close relation with the electronic structure of the two different molecular systems. We show that a vibronic coupling mechanism involving the hydrogen bond protons and the electrons on theπ-electronic systems in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the carboxylic acid dimers occurs. A strong coupling in2-furanacrylic aciddimers prefers a “tail-to-head-”typeDavydov couplingwidespread by theπ-electrons. A weakthrough-spacecoupling in2-furanacetic aciddimers is responsible for a “side-to-side-” type coupling. The relative contribution of each exciton coupling mechanism in the dimer spectra generation is temperature and the molecular electronic structure dependent. This explains the observed difference in the temperature-induced evolution of the compared spectra.

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