Quantifying solvent effects through QSPR: A new look over different model equations

The heterolysis reactions of 3 tertiary alkyl halides (2-chloro-2-methylpropane, 2-bromo-2-methylpropane and 3-bromo-3-ethylpentane) in a set of 21 protic and aprotic solvents, representative of various classes of solvents, were used to study solvent effects upon reactivity, at 298.15 K. Quantitative Structure-Property Relationships established through the use of multiple linear regressions, namely a model equation based on the solvatochromic parameters π*, α and β (the KAT equation), was shown to provide robust and predictive quantifications of the main solute-solvent interactions which prevail in the studied reaction processes. Changes in the departing halogen and in the size of the carbonated skeleton induce well quantified sensitivities to each solvent descriptor depending on the type of interaction being modeled. Other model equations were tested, and results evidenced some weaknesses related to inadequate solvent description ability or ill-conceived scales' use.