Thermodynamic and Kinetic Studies of the Activities of Aldehydic C−H Bonds toward Their H‐Atom Transfer Reactions

Abstract

AbstractAldehydes can not only accept hydrogen atoms to be reduced to alcohols, showing their oxidation properties; but also can donate hydrogen atoms of the C(sp2)−H bonds as hydrogen atom donors, showing their reduction properties. In this article, the hydrogen atom transfer reactions of eight aldehydes and free radicals in acetonitrile at 298 K were studied. The thermo‐kinetic parameters ΔG≠°(XH) of C(sp2)−H bonds in aldehydes were obtained by ΔG≠XH/Y=ΔG≠°(XH)+ΔG≠°(Y) as the ΔG≠°(Y) of free radicals were available in our previous work. The bond dissociation free energies ΔGo(XH) of C(sp2)−H bonds were calculated by iBonD HM method. The intrinsic resistance energies ΔG≠XH/X were determined as the ΔG≠°(XH) and ΔGo(XH) were available. ΔGo(XH), ΔG≠XH/X, and ΔG≠°(XH) were used to access the H‐donating abilities of C(sp2)−H bonds in aldehydes in thermodynamics, kinetics and actual HAT reactions. The scales and the effect of the structures of aldehydes on ΔGo(XH), ΔG≠XH/X, and ΔG≠°(XH) were discussed carefully. The oxidizing and reducing abilities of aldehydes, and the comparison of H‐donating abilities between C(sp2)−H of aldehydes with C(sp3)−H of the corresponding alcohols were also researched in detail. This paper not only fills the gap in the study of H‐donating activities of aldehydic C−H bonds, but also provides data support for the design and synthesis of more C(sp2)−H type antioxidants.