Easy Access to Experimental Bond Dissociation Energies in Solution Using 2D-IR Spectroscopy

Bond dissociation free energies (BDFEs) of X─H bonds are central for the thermodynamics of proton-coupled electron transfer (PCET) and hydrogen-atom transfer (HAT) reactions, yet their direct determination in solution remains experimentally challenging. Established approaches rely on radical equilibration against reference compounds, or on multi-step thermodynamic cycles that compound experimental and computational uncertainties, and are often restricted to a narrow range of solvents. Here, we introduce two-dimensional infrared (2D-IR) spectroscopy as a direct spectroscopic route to BDFEs of main-group hydrides. Analysing the observed anharmonic signatures of the X─H stretching mode within the Morse potential framework yields the spectroscopic dissociation energy ( $D_0$ ), and hence the BDE and BDFE, from a single experiment. We validate this approach on a series of silanes ( ${\mathrm{Ph}}_3\mathrm{SiH}$ , ${\mathrm{Et}}_3\mathrm{SiH}$ , ${\mathrm{Cl}}_3\mathrm{SiH}$ , ${\mathrm{Mes}}_3\mathrm{SiH}$ ) across solvents of widely varying polarities and hydrogen bond basicities (ranging from cyclohexane to DMSO), and benchmark the results against DFT, and higher-level detailed potential energy curve scans. Furthermore, a survey of other X─H/X─D bonds (e.g., Ge─H, Sn─H, O─H/O─D and S─H) reveals the general applicability of this method. Requiring only two well-defined observables and providing simultaneous access to solvation effects, our method establishes 2D-IR as a quantitative thermochemical tool.