Electrosynthesis is emerging as a powerful strategy for building C–N bonds using renewable electricity in place of stoichiometric oxidants, reductants, or hazardous reagents. Yet the central challenge in electrifying multi-step organic transformations lies in achieving selective control over reactive intermediates that form and evolve at the electrode interface. Operando infrared (IR) spectroscopy has become a key tool in addressing this challenge. By probing vibrational fingerprints directly during electrochemical operation, IR spectroscopy reveals transient species, parallel pathways, and competing reactions that dictate the efficiency and selectivity of C–N bond-forming electrosynthesis. Across various systems—including alcohol-to-amine conversion, reductive amination, and N-formylation—operando IR studies have provided mechanistic clarity that cannot be obtained from electrochemical data alone.

In electrocatalytic oxidation of alcohols followed by reductive amination, operando IR monitoring enables direct observation of aldehyde formation during the oxidation of benzyl alcohol on nickel oxyhydroxide surfaces. The appearance of the C=O stretching mode of benzaldehyde under controlled potentials allows the reaction sequence to be mapped in real time, capturing the transition from alcohol to aldehyde before further oxidation can occur. IR spectra also help distinguish selective aldehyde formation from overoxidation to carboxylates, which display characteristic carboxylate stretching bands. This information guides the optimization of catalyst loading, potential windows, and electrolyte conditions to maximize aldehyde selectivity. During the subsequent reductive amination step, IR detection of imine-related vibrations confirms formation of the aldimine intermediate and its potential-dependent conversion to the amine product. These spectroscopic signatures connect anodic and cathodic steps, illustrating how paired electrolysis can be tuned for efficient alcohol-to-amine conversion.

IR spectroscopy also plays a decisive role in elucidating mechanistic complexity during the electrochemical N-formylation of amines using methanol as both solvent and carbon source. In these systems, methanol oxidation first produces formaldehyde, which forms a hemiaminal upon reaction with an amine. Operando IR spectra reveal not only the expected aldehyde and hemiaminal features, but also additional bands corresponding to highly reactive intermediates. Detailed comparison of potential-resolved spectra has shown that these features are consistent with the formation of an isocyanide species—an intermediate typically associated with harsh dehydration chemistry. Confirmatory experiments demonstrate that this reactive intermediate can be generated and consumed entirely within the controlled electrochemical environment. Thus, IR spectroscopy establishes the existence of dual mechanistic pathways: direct oxidation of the hemiaminal to the formamide, and an isocyanide-mediated sequence that ultimately converges to the same product. Such mechanistic branching would remain hidden without real-time spectroscopic observation.

More broadly, operando IR spectroscopy provides mechanistic insight that shapes the design principles of sustainable C–N bond formation. It enables differentiation between surface-mediated and solution-phase reactions, helps identify the onset of undesired side processes such as hydrogen evolution or overoxidation, and reveals how pH, electrode material, and applied potential shift intermediate lifetimes and reaction equilibria. By correlating IR signals with faradaic efficiencies and product distributions, reaction conditions can be rationally optimized for selectivity.

Together, these studies show that operando IR spectroscopy is not merely a diagnostic tool but a foundational technique for advancing green electrosynthesis. By illuminating the molecular choreography of intermediates at electrified interfaces, IR spectroscopy enables the development of efficient, selective, and sustainable routes to amines, formamides, and other nitrogen-containing products via C–N bond formation.