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

ABSTRACT

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 (), and hence the BDE and BDFE, from a single experiment. We validate this approach on a series of silanes (, , , ) 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.