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Issue 34, 2016
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Accurate thermodynamic properties of gas phase hydrogen bonded complexes

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Abstract

We have measured the infrared spectra of ethanol·dimethylamine and methanol·dimethylamine complexes in the 299–374 K temperature range, and have determined the enthalpy of complex formation (ΔH) to be −31.1 ± 2 and −29.5 ± 2 kJ mol−1, respectively. The corresponding values of the Gibbs free energy (ΔG) are determined from the experimental integrated absorbance and a calculated oscillator strength of the OH-stretching vibrational transition to be 4.1 ± 0.3 and 3.9 ± 0.3 kJ mol−1 at 302 and 300 K, respectively. The entropy, ΔS is determined from the values of ΔH and ΔG to be −117 ± 7 and −111 ± 10 J (mol K)−1 for the ethanol·dimethylamine and methanol·dimethylamine complexes, respectively. The determined ΔH, ΔG and ΔS values of the two complexes are similar, as expected by the similarity to their donor molecules ethanol and methanol. Values of ΔH, ΔG and ΔS in chemical reactions are often obtained from quantum chemical calculations. However, these calculated values have limited accuracy and large variations are found using different methods. The accuracy of the present ΔH, ΔG and ΔS values is such that the benchmarking of theoretical methods is possible.

Graphical abstract: Accurate thermodynamic properties of gas phase hydrogen bonded complexes

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Publication details

The article was received on 04 Jul 2016, accepted on 04 Aug 2016 and first published on 04 Aug 2016


Article type: Paper
DOI: 10.1039/C6CP04648G
Citation: Phys. Chem. Chem. Phys., 2016,18, 23831-23839
  • Open access: Creative Commons BY-NC license
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    Accurate thermodynamic properties of gas phase hydrogen bonded complexes

    A. S. Hansen, Z. Maroun, K. Mackeprang, B. N. Frandsen and H. G. Kjaergaard, Phys. Chem. Chem. Phys., 2016, 18, 23831
    DOI: 10.1039/C6CP04648G

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