Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3030 Heverlee, Belgium
Abstract:
In previous publications [1–3], we have been concerned with the influence of hydrogen bond formation on the Raman intensity of the carbonyl stretching vibration. It has been shown that hydrogen bond association of simple carbonyl bases (cyclohexanone, acetone, acetophenone) with proton donors such as phenol derivatives, hydrochlorid or hydrobromic acid brings about an intensity increase of the νCO Raman band; moreover, the intensity enhancement is linearly related to the enthalpy of complex formation. In the present work, these measurements are extended to the complexes formed between methyl acetate (MeAc) and phenol derivatives.
![/></figure>As suggested by the frequency lowering of the ν<sub>CO</sub> vibration and the frequency increase of the ν<sub>CO</sub> band, complex formation in solution takes place on the carbonyl function.From NMR [4–5] and UV data [6] it can also be concluded that protonation via hydrogen-bonded attachment occurs in solution predominantly at the carbonyl oxygen atom.Literature data for the thermodynamic quantities referring to esters with hydroxylic compounds are scarce. Consequently in this work, we have determined the equilibrium constants and the enthalpy of formation for complexes between MeAc and phenol derivatives. We also report the absolute intensity of the ν<sub>CO</sub> Raman band in the free ester molecule and in the complexes, all measurements been made in a solvent of low polarity : carbontetrachloride.</td>
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