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

摘要

Aldehydes can not only accept hydrogen atoms to be reduced to alcohols, showing their oxidation properties; but also can donate hydrogen atoms of the C(sp(2))-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 Delta G(not equal)degrees(XH) of C(sp(2))-H bonds in aldehydes were obtained by Delta G(XH/Y)(not equal)=Delta G(not equal)degrees(XH)+Delta G(not equal)degrees(Y) as the Delta G(not equal)degrees(Y) of free radicals were available in our previous work. The bond dissociation free energies Delta G(o)(XH) of C(sp(2))-H bonds were calculated by iBonD HM method. The intrinsic resistance energies Delta G(XH/X)(not equal) were determined as the Delta G(not equal)degrees(XH) and Delta G(o)(XH) were available. Delta G(o)(XH), Delta G(XH/X)(not equal), and Delta G(not equal)degrees(XH) were used to access the H-donating abilities of C(sp(2))-H bonds in aldehydes in thermodynamics, kinetics and actual HAT reactions. The scales and the effect of the structures of aldehydes on Delta G(o)(XH), Delta G(XH/X)(not equal), and Delta G(not equal)degrees(XH) were discussed carefully. The oxidizing and reducing abilities of aldehydes, and the comparison of H-donating abilities between C(sp(2))-H of aldehydes with C(sp(3))-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(sp(2))-H type antioxidants.