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 Ka) 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.