Hydrogen Bonding of Water in Aqueous Alcohol Solution : Spectral Analyses by an Extended Concept of Molar Absorption Coefficient

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  • Ikehata Akifumi
    National Food Research Institute, National Agriculture and Food Research Organization (NARO)

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Other Title
  • アルコール水溶液中の水の水素結合‐モル吸光係数の拡張概念によるスペクトル解析‐
  • 年間特集「水」 アルコール水溶液中の水の水素結合--モル吸光係数の拡張概念によるスペクトル解析
  • ネンカン トクシュウ ミズ アルコール スイヨウエキチュウ ノ ミズ ノ スイソ ケツゴウ モル キュウコウ ケイスウ ノ カクチョウ ガイネン ニ ヨル スペクトル カイセキ

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Abstract

The hydration of monovalent alcohols (methanol, ethanol, 1-propanol, 2-propanol and tert-butanol), which are perfectly soluble in water, has been studied by using near infrared spectroscopy by focusing on stretching vibrations of each component at around 7000 cm−1. The absorbance of the band ordinarily does not obey Beer's law because of the presence of intermolecular interactions, e.g. hydrogen bonding. To estimate the spectra of non-ideal solutions, such as water-alcohol mixtures, partial molar absorptivity (PMA) is newly proposed as an extended concept of conventional molar absorption coefficient. A PMA is defined as the concentration differentiation of absorbance. Subsequently, the non-ideal spectral components, called excess partial molar absorptivity (EPMA), are calculated by subtraction between real and ideal molar absorption spectra. EPMA reveals the hidden absorption peaks assigned to different hydrogen-bonding species. By careful examination of PMA and EPMA spectra, strengthening of hydrogen bonding is found in low alcohol range less than a well-known breakpoint at around 25 mass% as a result of hydration to the solute molecules. In a concentration range higher than the breakpoint, water and alcohol tend to be separated into each small domain. These results are common in the monovalent alcohol - water binary mixtures.

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 59 (1), 13-21, 2010

    The Japan Society for Analytical Chemistry

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