Self-association and picosecond dynamics in liquid dimethyl sulfoxide

Area of Science:

• Physical Chemistry
• Spectroscopy
• Liquid State Physics

Background:

• Dimethyl sulfoxide (DMSO) is a widely used solvent, yet its self-association behavior and hydrogen bonding characteristics remain poorly understood.
• Previous studies on liquid DMSO association equilibriums are limited, and the enthalpy of self-association has not been determined.

Purpose of the Study:

• To investigate self-association equilibriums in neat liquid DMSO across a range of temperatures.
• To determine the enthalpy of DMSO self-association.
• To clarify the role and presence of hydrogen bonding in liquid DMSO.

Main Methods:

• Raman spectroscopy was employed to study self-association equilibriums in liquid DMSO at various temperatures.
• Analysis of time correlation functions for vibrational dephasing and reorientation of monomers and dimers was performed.
• C-S-C and C-H symmetric vibrations were utilized to probe molecular dynamics.

Main Results:

• No evidence of hydrogen bonding was detected in liquid DMSO.
• Association constants for DMSO self-association were determined, ranging from 0.20 L mol(-1) at 23 °C to 0.081 L mol(-1) at 100 °C.
• The enthalpy of DMSO self-association was calculated to be -11.7 ± 0.9 kJ mol(-1).

Conclusions:

• The study provides the first experimental determination of the enthalpy of self-association for DMSO.
• The findings indicate that hydrogen bonding is not a significant factor in DMSO self-association.
• The determined association constants and enthalpy offer crucial data for understanding DMSO's behavior as a solvent and reaction medium.