CMIRS Solvation Model for Methanol: Parametrization, Testing, and Comparison with SMD, SM8, and COSMO-RS

Abstract

The new continuum solvation model, composite method for implicit representation of solvent (CMIRS), proposed by Pomogaeva and Chipman and implemented in GAMESS was parametrized for methanol solvent, with the aim of using it for ionic reactions in solution. The model was tested for predicting single-ion solvation free energy, pK of acids and protonated bases, and the activation free-energy barriers of S2 and SAr reactions in methanol. A comparison was performed with other continuum models, such as SMD, SM8, and COSMO-RS. For a prediction of pK and free-energy barriers, the order of performance was CMIRS > COSMO-RS > SMD > SM8. In particular, the CMIRS model is much superior to the other continuum models for predicting pK of acids (without empirical corrections) and is able to evenly describe hard ions like methoxide and charge-dispersed ions like 2,4,6-trinitrophenol. On the basis of our results, we suggest that the field-extremum contribution, present in CMIRS, should be included in continuum solvation models, which can result in substantial improvement in the modeling of ionic reactions in solution.

Hybrid discrete‐continuum solvation methods

“…The continuum solvation models generally yield good results for reactions of neutral species or even anion‐molecule reactions in aprotic solvents, because no strong solute–solvent interactions are usually present . However, in the case of many ionic reactions in protic solvents or formation of species with strong solute–solvent interaction, pure continuum solvation models can lead to substantial error . A very interesting and recent example of this can be found in the efforts to model correctly the well‐known Morita‐Baylis‐Hillman reaction that proceeds through a zwitterionic intermediate .…”

Cleaving paraoxon with hydroxylamine: Ammonium oxide isomer favors a Frontside attack mechanism

“…Hence, the SM8 method predicts that both the mechanisms are taking place. The reason for selecting SMD as the reference method was that recent comparisons between SMD and SM8 for ionic reactions have indicated that SMD is much more reliable . Consequently, our results indicated that the current view of the mechanism as taking place by means of backside attack is not correct.…”

“…A more reliable method, using an explicit solvent, was used to investigate this equilibrium, and it was found that a better description was obtained with the SM8 method, rather than the SMD method . Nevertheless, recent studies of anion‐molecule nucleophilic substitution reactions have indicated that SMD outperforms SM8 for reaction barriers in methanol solvent . Considering that in the transition state there is a partial desolvation of hydroxylamine in the zwitterion form, the error of SMD should decrease.…”

A computational study on the identity of the active catalyst structure for Ru(ii) carboxylate assisted C–H activation in acetonitrile

“…Although this difference is still not perfect, as the free energy for formation of charges species (from neutral) is difficult to predict when using continuum solvation models that compensate the high energy required to dissociate the ions with large solvation free energies, thereby underestimating the solvation of a ion pair (cation and anion) in polar solvents like acetonitrile and methanol. 29,30 It is only when combining Gibbs free energy with a thermal correction, a dispersion energy correction and a larger basis set energy that the value becomes 2.8 kcal mol −1 . Missing any one of these methodology steps could lead to the rejection of cationic pathways as viable mechanistic pathways in a computational study.…”