Reichardt’s Dye-Based Solvent Polarity and Abraham Solvent Parameters: Examining Correlations and Predictive Modeling

Abstract

The concept of “solvent polarity” is widely used to explain the effects of using different solvents in various scientific applications. However, a consensus regarding its definition and quantitative measure is still lacking, hindering progress in solvent-based research. This study hopes to add to the conversation by presenting the development of two linear regression models for solvent polarity, based on Reichardt’s ET(30) solvent polarity scale, using Abraham solvent parameters and a transformer-based model for predicting solvent polarity directly from molecular structure. The first linear model incorporates the standard Abraham solvent descriptors s, a, b, and the extended model ionic descriptors j+ and j−, achieving impressive test-set statistics of R2 = 0.940 (coefficient of determination), MAE = 0.037 (mean absolute error), and RMSE = 0.050 (Root-Mean-Square Error). The second model, covering a more extensive chemical space but only using the descriptors s, a, and b, achieves test-set statistics of R2 = 0.842, MAE = 0.085, and RMSE = 0.104. The transformer-based model, applicable to any solvent with an associated SMILES string, achieves test-set statistics of R2 = 0.824, MAE = 0.066, and RMSE = 0.095. Our findings highlight the significance of Abraham solvent parameters, especially the dipolarity/polarizability, hydrogen-bond acidity/basicity, and ionic descriptors, in predicting solvent polarity. These models offer valuable insights for researchers interested in Reichardt’s ET(30) solvent polarity parameter and solvent polarity in general.

Conventional and Green Rubber Plasticizers Classified through Nile Red [E(NR)] and Reichardt’s Polarity Scale [ET(30)]

“…As expected, polar polymers are appropriately positioned in the E(NR) scale, with epoxidized natural rubber (ENR- 25) showing an E(NR) value of 54.32 kcal/mol with respect to 57.55 kcal/mol of liquid IR and 56.82 kcal/mol of the solid film of IR.…”

“…In fact, protonation of the E T (30) dye destroys the CT band of this solvatochromic dye. To circumvent such a situation, other authors [25] have proposed an interesting, original and sophisticated approach that permits the estimation of the E T (30) values of certain "difficult" substrates where the direct polarity measurement is hindered. The alternative approach proposed in the present work is to use Nile Red dye as a solvatochromic dye.…”

“…In a seminal paper belonging to this Special Issue of "Liquids", Acree and Lang [25] have shown an interesting and sophisticated approach that permits the estimation of the E T (30) values of certain "difficult" substrates where the direct polarity measurement is hindered for a series of reasons, as in the present case for apolar polymers (e.g., rubbers) and certain plasticizers.…”

From a humorous post to a detailed quantum-chemical study: isocyanate synthesis revisited

“…The latter one was introduced by Reichardt et al in 1963 and since then has been extensively used for studies involving solvent polarity. [31][32][33][34][35] The full list of the studied solvents, as well as the corresponding dielectric constant and Reichardt's parameter values, can be found in the ESI. † The correlations of the effective barrier heights (eqn (2)) with solvents' dielectric constants e and Reichardt's E T (30) parameters are shown in Fig.…”

From Humorous Post to Detailed Quantum-Chemical Study: Isocyanate Synthesis Revisited

“…The latter one was introduced by Reichardt et al in 1963 and since then has been extensively used for studies involving solvent polarity. [31][32][33][34][35] The full list of the studied solvents, as well as the corresponding dielectric constant and Reichardt's parameter values, can be found in ESI. The correlations of the effective barrier heights (Equation 2) with solvents' dielectric constants ε and Reichardt's E T (30) parameters are shown in the Figure 6.…”