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Significant substitution effects in dipolar and non-dipolar supercritical fluids
Daisuke Kajiya1, Ken-ichi Saitow
1Natural Science Center for Basic Research and Development (N-BARD), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
The Journal of Chemical Physics
|June 28, 2011
Summary
Studying vibrational Raman spectra of ethylene derivatives in supercritical fluids revealed significant solute-solvent interactions. The absence of steric hindrance in trans-stilbene enhances local density and influences solvation structures.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Supercritical Fluids
Background:
- Vibrational Raman spectroscopy probes molecular vibrations.
- Supercritical fluids exhibit tunable properties with density.
- Solvation structure influences molecular interactions and spectra.
Purpose of the Study:
- To investigate the influence of solute structure on vibrational Raman spectra in supercritical fluids.
- To quantify the effect of steric hindrance on solvation and local density.
- To compare solvation in dipolar and non-dipolar supercritical solvents.
Main Methods:
- Measurement of vibrational Raman spectra for ethylene derivatives (cis-C2H2Cl2, cis-stilbene, trans-stilbene).
- Experiments conducted in supercritical CHF3 and CO2 along an isotherm at varying densities.
- Theoretical analysis of spectral shifts and solvation structures.
Main Results:
- Significant differences in Raman shifts observed among solutes, up to 20 times.
- Trans-stilbene exhibited exceptionally large Raman shifts, comparable to hydrogen-bonded systems.
- Site-selective solvation around the phenyl group, driven by dispersion forces, was identified.
- Absence of steric hindrance in trans-stilbene led to significant local density augmentation.
Conclusions:
- Steric hindrance plays a crucial role in determining solvation structures in supercritical solutions.
- Raman spectroscopy effectively quantifies solute-solvent interactions and local density effects.
- Findings provide novel insights into solvation dynamics in supercritical environments.
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