London Dispersion in Alkane Solvents

Area of Science:

• Physical chemistry
• Supramolecular chemistry
• Computational chemistry

Background:

• The role of London dispersion interactions in molecular structure and stability is well-established.
• However, the extent to which these interactions are attenuated in solution remains poorly understood.
• Current quantitative data primarily come from computational studies.

Purpose of the Study:

• To experimentally investigate the influence of London dispersion interactions in solution.
• To provide empirical data for incorporating dispersion effects into solution-phase molecular design.
• To examine how solvent properties affect intramolecular dispersion using a tailored molecular probe.

Main Methods:

• Utilized an azobenzene derivative as a molecular probe to study dispersive interactions.
• Systematically varied alkyl substituents at meta positions of the azobenzene core.
• Measured the half-lives of thermally induced Z to E isomerization in various alkane solvents.
• Correlated changes in isomerization half-lives with solvent properties and probe structure.

Main Results:

• Intramolecular dispersion effects were found to be only marginally influenced by the experimental setup.
• Solvents with lower surface tension led to increased half-lives (up to 20%) due to reduced destabilizing solvent-solvent interactions.
• Specific interactions between the probe's alkyl chains and solvent molecules caused additional fluctuations in half-lives.

Conclusions:

• Experimental evidence suggests that London dispersion interactions in solution are sensitive to solvent characteristics.
• Solvent-induced changes in the conformer ensemble likely contribute to observed fluctuations in isomerization rates.
• This study provides valuable experimental insights into the behavior of dispersion forces in solution, complementing computational findings.