The paper presents our experience in the combined use of vibrational spectroscopy and dielectric methods in the investigation of molecular structure and interactions in hydrogen-bonded systems. Here, we show three selected examples obtained by our research groups. The first example concerns examination of the mixture of propionic acid with triethylamine. It has been found the presence of the pronounced maxima of dielectric permittivity and conductivity at some acid-amine molar ratio. This observation suggests that the mixture has properties of both the ionic and dipolar liquids. In the next work, we have elucidated the mechanism of the dissociation of 1-octanol and 3-octanol associates in solutions and in the pure liquid phase. It has been evidenced that at first dissociate the terminal alcohol molecules. These studies also have shown that the tendency of formation of the cyclic associates increases from 1-octanol to 3-octanol. The last example concerns an examination of 1-hexanol in n-hexane. Our results suggest that in the solutions the most populated species are the cyclic trimers. It is contrary to numerous previous studies claiming that cyclic tetramers are the most abundant species. Of particular importance is the observation that the peak due to the free OH is contributed mainly by the absorption from the monomers. This suggests that the band from the free terminal O-H groups in the linear associates is obscured by a broad absorption from the hydrogen-bonded O-H groups. Based on our results, it is possible to conclude that simultaneous use of vibrational spectroscopy and dielectric methods allows to get deeper insight into molecular structure with higher confidence and to draw conclusions not available from separate application of each method.

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