2 research outputs found

    C–H···O Interaction in Methanol–Water Solution Revealed from Raman Spectroscopy and Theoretical Calculations

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    A combination of temperature-dependent Raman spectroscopy and quantum chemistry calculation was employed to investigate the blue shift of CH<sub>3</sub> stretching vibration in methanol–water mixtures. It shows that the conventional O–H···O hydrogen bonds do not fully dominate the origin of the C–H blue shift and the weak C–H···O interactions also contribute to it. This is consistent with the temperature-dependent results, which reveal that the C–H···O interaction is enhanced upon increasing the temperature, leading to further C–H blue shift in observed spectra at high temperature. This behavior is in contrast with the general trend that the conventional O–H···O hydrogen bond is destroyed by the temperature. The results will shed new light onto the nature of the C–H···O interaction and be helpful to understand hydrophilic and hydrophobic interactions of amphiphilic molecules in different environments

    Identification of Alcohol Conformers by Raman Spectra in the C–H Stretching Region

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    The spontaneous polarized Raman spectra of normal and deuterated alcohols (C<sub>2</sub>–C<sub>5</sub>) have been recorded in the C–H stretching region. In the isotropic Raman spectra, a doublet of −C<sub>α</sub>H stretching vibration is found for all alcohols at below 2900 cm<sup>–1</sup> and above 2950 cm<sup>–1</sup>. By comparing the experimental and calculated spectra of various deuterated alcohols, the doublets are attributed to the −C<sub>α</sub>H stretching vibration of different conformers. For ethanol, the band observed at 2970 cm<sup>–1</sup> is assigned as the stretching vibration of −C<sub>α</sub>H in the C<sub>α</sub>–O–H plane of the <i>gauche-</i>conformer, while the band at 2895 cm<sup>–1</sup> is contributed from both the −C<sub>α</sub>H<sub>2</sub> symmetrical stretching vibration of the <i>trans-</i>conformer and the −C<sub>α</sub>H stretching vibration out of the C<sub>α</sub>–O–H plane of the <i>gauche-</i>conformer. The population of <i>gauche</i>-conformer is estimated to be 54% in liquid ethanol. For the larger alcohols, the same assignments for the doublet are obtained, and the populations of <i>gauche</i>-conformers with plane carbon skeleton are found to be slightly larger than that of ethanol, which is consistent with results from molecular dynamics simulations
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