A thermodynamic study of selective solvation in solvent mixtures

Area of Science:

• Physical Chemistry
• Solution Chemistry
• Spectroscopy

Background:

• Understanding solvent effects is crucial for chemical processes.
• Preferential solvation describes the non-uniform distribution of solvent molecules around a solute.
• Tri-n-butylphosphine oxide is a sensitive probe for studying solvation dynamics.

Purpose of the Study:

• To thermodynamically quantify preferential solvation in binary solvent mixtures.
• To determine H-bond donor parameters for various solvents.
• To investigate the interplay between specific and non-specific solvent interactions.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, specifically (31)P NMR chemical shift measurements.
• Analysis using a model separating specific H-bond and non-specific bulk solvent effects.
• Determination of equilibrium constants for solvated states.

Main Results:

• Preferential solvation was thermodynamically quantified for several binary solvent mixtures.
• H-bond donor parameters (alpha) were determined for a range of solvents.
• Identical H-bond donor parameters were observed for solvents acting as solutes and solvents.
• Alkanes exhibited larger H-bond donor parameters than predicted, suggesting increased van der Waals interactions.

Conclusions:

• The study validates the interchangeability of solute and solvent H-bond donor parameters.
• The electrostatic solvent competition model provides a framework for understanding these interactions.
• Van der Waals forces play a more significant role in solvation for alkanes than electrostatic effects alone suggest.