Intramolecular Hydrogen Atom Transfer in Aminyl Radical at Room Temperature with Large Kinetic Isotope Effect.

We report a large kinetic isotope effect at 298 K, kH /kD ≈ 150, associated with an intramolecular 1,5-hydrogen atom transfer (1,5-HAT) in the decay of a PEGylated carbazyl (aminyl) radical in solution. The experimental observations surprisingly combine the hallmarks of tunneling, including large KIEs and unusual activation parameters, with linear Arrhenius and Eyring plots over an exceptionally wide temperature range of 116 K.