Single solvent molecules can affect the dynamics of substitution reactions

Abstract

Solvents have a profound influence on chemical reactions in solution and have long been used to control their outcome. Such effects are generally considered to be governed by thermodynamics; however, little is known about the steric effects of solvent molecules. Here, we probe the influence of individual solvent molecules on reaction dynamics and present results on the atomistic dynamics of a microsolvated chemical reaction—the fundamentally important nucleophilic substitution reaction. We study the reaction of OH− with CH3I using a technique that combines crossed-beam imaging with a cold source of microsolvated reactants. Our results reveal several distinct reaction mechanisms for different degrees of solvation; surprisingly, the classical co-linear substitution mechanism only dominates the dynamics for mono-solvated reactants. We analyse the relative importance of the different mechanisms using ab initio calculations and show that the steric characteristics are at least as relevant as the energetics in understanding the influence of solvent molecules in such microsolvated reactions. How do solvent molecules influence the dynamics of a chemical reaction? Crossed-beam molecular imaging experiments reveal how different reaction mechanisms can be either suppressed or enhanced by the presence of one water molecule. The study finds that steric effects are responsible for the observed dynamics.

Cite this article

Otto, R., Brox, J., Trippel, S. et al. Single solvent molecules can affect the dynamics of substitution reactions. Nature Chem 4, 534–538 (2012). https://doi.org/10.1038/nchem.1362

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