LAUSR

Abstract The mechanistic origin of the hydrogen-abstraction reactivity of hydroxyimide organocatalysts in three types has been theoretically explored by intrinsic reaction coordinate and distortion/interaction model. All these H-abstraction processes can be divided into two parts: C H bond approaching to catalyst and subsequent breaking via a cross-point structure. Generally, the H-abstraction reactivity increase when a catalyst has small LUMOcatalyst-HOMOsubstrate gap, C H bond approaching energy and distortion energy required to achieve its transition state (TS) geometry, and large electron affinity. The TS structures for 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO ) and N-methyl benzohydroxamic acid (NMBHA) are inclined to be product-like, but much reactant-like for N-hydroxyphthalimide (NHPI)-type catalysts.