Progress toward reaction monitoring at variable temperatures: a new stopped‐flow NMR probe design

A stopped‐flow NMR probe is described that enables fast flow rates, short transfer times, and equilibration of the reactant magnetization and temperature prior to reaction. The capabilities of the probe are demonstrated by monitoring the polymerization of lactide as catalyzed by the air‐sensitive catalyst 1,3‐dimesitylimidazol‐2‐ylidene (IMes) over the temperature range of −30 to 40 °C. The incorporation of stopped‐flow capabilities into an NMR probe permits the rich information content of NMR to be accessed during the first few seconds of a fast reaction.