Hydrogen abstraction from H‐donor substrates by the 6‐CF₃‐benzotriazol‐N‐oxyl radical (TFNO)

Abstract

The aminoxyl radical 6-trifluoromethyl-benzotriazol-N-oxyl (TFNO) has been generated from the parent hydroxylamine 6-CF3-1-hydroxy-benzotriazole (TFBT) by one-electron oxidation with a Ce-IV salt and characterized by spectrophotometry and cyclic voltammetry (CV). Rate constants of H-abstraction (k(H)) by TFNO from a number of H-donor benzylic substrates have been determined spectrophotometrically in MeCN solution at 25 degrees C. A radical H-atom transfer (HAT) route of oxidation is substantiated for TFNO by several pieces of evidence. The kinetic data also testify the relevance of stereoelectronic effects upon the HAT reactivity of TFNO. Copyright (C) 2010 John Wiley & Sons, Ltd

Importance of π-Stacking Interactions in the Hydrogen Atom Transfer Reactions from Activated Phenols to Short-Lived N-Oxyl Radicals

“…In the series of the substituted 4-X-PINOs ( 1 – 3 ) and 6-Y-BTNOs ( 4 – 6 ) it can be noted that substituents exert a significant effect on the rate constants for hydrogen transfer from all the phenolic substrates. The reactivity increases by increasing the electron-withdrawing properties of the aryl substituent as found in hydrogen abstraction processes from C–H bonds ,,,,,, in accordance with the influence of both enthalpic and polar effects. From an enthalpic point of view, it has to be considered that BDE NO‑H values regularly increase with increasing electron-withdrawing (EW) power of the aryl substituents. ,, The BDE NO‑H values calculated for 1H – 8H are reported in Table together with the calculated values reported for NHPI and 4-OCH 3 -NHPI − and the experimental values determined for 4-X-NHPIs and 6-Y-HBTs by the EPR and UV–vis radical equilibration technique. ,, …”