Bond Dissociation Free Energies in A Room-Temperature Ionic Liquid: Are Radical Species More Stable in an Ionic Liquid?

In this work, we established a method for the derivation of bond dissociation free energies (BDFEs) in an aprotic ionic liquid (IL), i.e., BmimNTf₂ (water content <15 ppm), at 298.15 K by combining equilibrium acidity (pKa) and oxidative potential (Eox). The method has an error bar of ±3 kcal mol⁻¹ based on the measurement uncertainties of pKa (H-A) and Eox (A⁻) in the IL. The BDFEs of 12 representative H-A bonds, including C-H, N-H, and O-H bonds, were measured in BmimNTf₂ and compared with those in DMSO. The results show that BDFEs of these H-A bonds in BmimNTf₂ are consistently and significantly lower (∼6.0 to 9.4 kcal mol⁻¹) than those in DMSO, indicating a pronounced weakening of these bonds in the ionic medium. Further thermodynamic analysis suggests that the lower BDFEs in BmimNTf₂ are likely due to the synchronous solvation stabilization of radical species (except H·) by the cation and anion of BmimNTf₂.