**4.3 Polarity and solvent effects**

Experimentally, the most common way to measure the polarity of a solvent is through its (bulk) dielectric constant (ε). The concept of polarity has been defined as the sum of all possible intermolecular interactions between the solvent and the solute, including specific interactions, for instance, HB effects, dipole-dipole, dipole-induced dipole, electron pair acceptor-electron pair donor, and acid-base interactions [1, 33]. Gazitúa et al. [12, 40] studied the solvation patterns of 21 COS and water over the reaction between 2,4-dinitrophenylsulfonyl chloride (DNBSCl) with SA amines in order to determine the solvent polarity effect on the reaction mechanism. Note that solvent polarity became relevant only in the reactions that proceeded by the non-catalyzed route. On this way, water and tetrahydrofuran

(THF) have a key role due to its ambiphilic character as an HB donor/acceptor that promotes a nucleophilic activation at the nitrogen center of the piperidine (nucleophile).
