London Dispersion in Alkane Solvents

The importance of London dispersion interactions in solution is an ongoing debate. Although the significance of dispersion for structure and stability is widely accepted, the degree of its attenuation in solution is still not properly understood. Quantitative evaluations are derived mostly from comp...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2021-01, Vol.60 (2), p.779-786
Main Authors: Strauss, Marcel A., Wegner, Hermann A.
Format: Article
Language:English
Subjects:
Alkanes
Attenuation
Azo compounds
azobenzene
Dispersion
Isomerization
London dispersion
molecular probe
solvent effects
Solvents
spectroscopy
Structural stability
Surface tension
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Summary:The importance of London dispersion interactions in solution is an ongoing debate. Although the significance of dispersion for structure and stability is widely accepted, the degree of its attenuation in solution is still not properly understood. Quantitative evaluations are derived mostly from computations. Experimental data provide guidelines to include London dispersion in solution phase design. Herein, dispersive interactions were examined with an azobenzene probe. Alkyl substituents in meta positions of the azobenzene core were systematically varied and the effect on the half‐lives for the thermally induced Z to E isomerization in several alkane solvents was determined. The results show that intramolecular dispersion is only marginally influenced. In solvents with low surface tension, reduced destabilizing solvent‐solvent interactions increase the half‐life up to 20 %. Specific individual interactions between alkyl chains on the azobenzene and those of the solvent lead to additional fluctuations of the half‐lives. These presumably result from structural changes of the conformer ensemble. The degree of attenuation of London dispersion in solution is evaluated. Dispersive interactions were examined with azobenzene probes. The effect on half‐lives for the thermally induced Z to E isomerization in several alkane solvents was determined. The results show only a marginally influence on intramolecular dispersion. In solvents with low surface tension, reduced destabilizing solvent‐solvent interactions increase the half‐life up to 20 %.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202012094