Self-Association and Picosecond Dynamics in Liquid Dimethyl Sulfoxide

Abstract

Dimethyl sulfoxide (DMSO) has been known for almost 150 years, but its properties as a solvent and reaction medium are far from being understood. In particular, association equilibriums in liquid DMSO have been characterized in just four papers, and the enthalpy of its self-association is unknown. The aims of this paper are to study self-association equilibriums in neat liquid DMSO at various temperatures by means of Raman spectroscopy, to find the enthalpy of self-association, and to solve the problem of hydrogen bonding in this liquid. Time correlation functions of vibrational dephasing and reorientation of coexisting monomers and dimers studied by the C-S-C and C-H symmetric vibrations indicate that external perturbations and vibrational and reorientational dynamics of these particles occur on different time scales. No signatures of H-bonding in DMSO are found. The association constants vary from 0.20 L mol(-1) (23 °C) to 0.081 L mol(-1) (100 °C). Their temperature dependence gives the enthalpy of association of DMSO as -11.7 ± 0.9 kJ mol(-1).

Proton transfer in a short hydrogen bond caused by solvation shell fluctuations: an ab initio MD and NMR/UV study of an (OHO)− bonded system

“…13 C enriched substances were used to shorten the experiment time and to lower the concentrations of the substances, which are beneficial if one wants to slow down molecular and proton exchange processes. Young valve; then the solvents were removed on a high vacuum line.…”

“…[5][6][7][8] Thermal fluctuations within the complex and its medium lead to a constant re-arrangement of the H-bond geometry and a distribution of rapidly interconverting structures is likely to be created. [12][13][14][15][16][17][18][19] Depending on the interacting partners and conditions several situations could be realized. 10,11 The lifetime of a solvatomer is limited by the rotational diffusion time and usually does not exceed 10 À9 s (often it lies in the picosecond time scale).…”

“…proton quantum delocalization, which is substantial in systems with low barriers and at low temperatures. The system has been studied experimentally by 1 H, 13 C NMR and UV-vis spectroscopy and theoretically by ab initio molecular dynamics and quantum-chemical calculations. 7, 8 and 61 in this work we have chosen a complex formed by para-nitrophenol with tetraethylammonium (TEA) acetate dissolved in a polar aprotic CD 2 Cl 2 -CDCl 3 mixture (Fig.…”

Phase Equilibria and Ionic Solvation in the Lithium Tetrafluoroborate–Dimethylsulfoxide System

“…In contrast with other similar studies, we described all equilibrium without exception, invoking for the analysis data on self-association of DMSO molecules in the liquid [31]. We proved that the solutions contained ions separated by solvent and contact ion pairs and presented for the fi rst time reliable evidence for H-bonds between the anions and DMSO.…”

“…A study of pure liquid DMSO led to the conclusion that its molecules did not tend to form H-bonds. A single line was observed in the region of the C-H symmetric stretching vibration [33]. Deconvolution of the spectra of the ionic solutions into components showed unambiguously that two lines appeared in them in this region (Fig.…”