Abstract
<jats:p>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 refer-ence 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 (D0), and hence the BDE and BDFE, from a single experiment. We validate this approach on a series of silanes (Ph3SiH, Et3SiH, Cl3SiH, Mes3SiH) across solvents of widely varying polarities and hydrogen bond basicities (ranging from toluene to DMSO), and benchmark the results against DFT, and higher-level detailed potential energy curve scans. Requiring only two well-defined observables and providing simultaneous access to solvation effects, our method establishes 2D-IR as a quantitative thermochemical tool.</jats:p>