Structure–activity relationship of alkanes and alkane derivatives for the abilities of C(sp³)H bonds toward their H‐atom transfer reactions

Abstract

Hydrogen atom‐donating ability of alkane is a research hotspot and has been extensively studied. In this article, the second‐order rate constants of 20 hydrogen atom transfer (HAT) reactions between aliphatic, benzylic, and allylic alkanes and alkane derivatives with CumO• in acetonitrile at 298 K were studied. The thermo‐kinetic parameter ΔG≠o(XH), bond dissociation free energy ΔGo(XH), and kinetic intrinsic resistance energy ΔG≠XH/X were determined and used to evaluate the H‐donating abilities of these substrates in thermodynamics, kinetics, and HAT reactions. Structure–activity relationships including the factors (electronic, stereoelectronic, and steric effects), introduction of CH3, Ph, or Cl in alkanes, and introduction of N atom in cycloalkane were discussed carefully. The results show that the order of H‐donating abilities is allylic alkanes > cycloalkanes > chain alkanes ≈ benzylic alkanes > haloalkanes. The introduction of CH3, Ph, or Cl in alkanes and the introduction of N atom to the carbon ring reduce ΔGo(XH) but increase ΔG≠XH/X, and ΔG≠o(XH) is the synthesis result of these two parameters. The reliability of ΔG≠o(XH) was verified, and the accuracy and reliability of the parameters were proved. Through the study of this paper, not only the ΔGo(XH), ΔG≠XH/X, and ΔG≠o(XH) of these alkanes and derivatives in HAT reaction can be quantitatively evaluated but also the structure–activity relationship of alkane is clearly researched.