Validation
of the Direct-COSMO-RS Solvent Model for
Diels–Alder Reactions in Aqueous Solution
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Abstract
The
modeling of chemical reactions in protic solvents tends to
be far more computationally demanding than in most aprotic solvents,
where bulk solvent effects are well described by dielectric continuum
solvent models. In the presence of hydrogen bonds from a protic solvent
to reactants, transition states or intermediates, a faithful modeling
of the solvent effects usually requires some kind of molecular dynamics
treatment. In contrast, the COSMO-RS (conductor-like screening model
for real solvents) approach has been known for about a decade to describe
protic solvent effects much better than continuum solvents, in spite
of being an implicit solvent model without explicit molecular dynamics.
More recently, the self-consistent use of its potential in electronic-structure
methods has led to the Direct-COSMO-RS approach. It allows, for example,
structure optimization in the presence of a protic solvent, of solvent
mixtures, as well as self-consistent property calculations. In view
of recent successful tests for electron transfer in organic mixed-valence
systems, in this work the wider applicability of D-COSMO-RS for organic
reactivity is evaluated by computation of activation and reaction
free energies, as well as transition-state structures of two prototypical
Diels–Alder reactions, with an emphasis on aqueous solution.
D-COSMO-RS indeed provides substantial improvements over the COSMO
continuum model and in judicious testing compares well with embedded
supermolecular model cluster treatments, without prior knowledge about
the average numbers of hydrogen-bonding interactions present