Accurate thermodynamic properties of gas phase hydrogen bonded complexes

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.

Room Temperature Gas-Phase Detection and Gibbs Energies of Water Amine Bimolecular Complex Formation

“…In comparison, the equilibrium constants of MeOH•DMA and MeOH•TMA have previously been determined with the combined theoretical and experimental approach used here. 24,33,61,62 For MeOH•DMA, a dual determination of K was obtained from the OH bstretching fundamental band and from the NH-stretching second overtone of the free NH stretch in the DMA acceptor molecule. For both bands, similar K values were obtained.…”

“…We have determined the equilibrium constant to be 0.13 ± 0.01 for H 2 O·DMA and 0.20 ± 0.02 for H 2 O·TMA (with the aforementioned potential error in the calculated intensities estimated to be less than 15%). In comparison, the equilibrium constants of MeOH·DMA and MeOH·TMA have previously been determined with the combined theoretical and experimental approach used here. ,,, For MeOH·DMA, a dual determination of K was obtained from the OH b -stretching fundamental band and from the NH-stretching second overtone of the free NH stretch in the DMA acceptor molecule. For both bands, similar K values were obtained.…”

Matrix isolation FTIR study of hydrogen-bonded complexes of methanol with heterocyclic organic compounds

“…A recent study about the thermodynamic properties of gas phase hydrogen bonded complexes has also conrmed that the OH-stretching vibration in the MeOH-DMA complex is temperature dependent. 58 More detailed information of the co-deposition of MeOH and pyrrole are shown in Fig. S2.…”

Vibrational study of methylamine dimer and hydrated methylamine complexes in solid neon supported by ab initio calculations

“…The high concentration of water in Earth's atmosphere makes its interactions with trace molecules important in atmosphere chemistry [2]. The polar NH 2 functional group in amines can form a strong hydrogen bond with water and alcohols and these complexes have given rise to many theoretical studies [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”