Tracking Propagating Perturbations in Chemical Reactions

Periodic perturbations, such as modulations of reactant concentration, propagate through chemical reactions with distinct phase delays. Tracking the propagation of such perturbations presents a powerful approach for probing the reaction connectivity and the rates of individual reaction steps, provided that high‐throughput and information‐rich analytical approaches are used. Here, the online monitoring of periodic perturbations in the organocatalytic addition of cyclopentadiene to α , β ‐unsaturated aldehydes by electrospray ionization–mass spectrometry (ESI–MS) is reported. Upon perturbation of input concentrations, ion intensities corresponding to substrates and reaction intermediates detected by ESI–MS exhibit characteristic time delays, providing insights into the kinetics of individual reaction steps, as supported by numerical simulations. This study provides a novel framework for online reaction monitoring and mechanistic analysis in chemical systems.