Quantitative evaluation of the actual hydrogen atom donating activities of O–H bonds in phenols: structure–activity relationship

Abstract

The H-donating activity of phenol and the H-abstraction activity of phenol radicals have been extensively studied.

Quantitative evaluation of H-donating abilities of C(sp3)–H bonds of nitrogen-containing heterocycles in hydrogen atom transfer reaction

“…A visual comparison of the Δ G ≠o (XH) values of the ɑ-C(sp 3 )–H bonds in 28 nitrogen-containing heterocycles and other H-donors in acetonitrile at 298 K is shown in Scheme 2. As discussed in our previous reports, 13–16 Δ G ≠o (XH) can be used as the characteristic physical parameter of XH to quantitatively evaluate its H-donating ability. The smaller the Δ G ≠o (XH) value of XH, the stronger its H-donating ability.…”

“…According to the definition of Δ G ≠o (XH), it consists of 1/2 the sum of Δ G o (XH) and Δ G ≠ XH/X . 13–16 In this work, Δ G o (XH) was calculated using the iBonD HM method 15 c ,16,20–22 to evaluate the thermodynamic H-donating potential of the substrate. Δ G ≠ XH/X was determined using the definition Δ G ≠o (XH) {Δ G ≠o (XH) = 1/2[Δ G ≠ XH/X + Δ G o (XH)]} and employed to evaluate the kinetic H-donating ability of the substrate.…”

“…Δ G ≠ XH/X was determined using the definition Δ G ≠o (XH) {Δ G ≠o (XH) = 1/2[Δ G ≠ XH/X + Δ G o (XH)]} and employed to evaluate the kinetic H-donating ability of the substrate. 13–16…”

“…, the thermo–kinetic parameter Δ G ≠o , was used to quantitatively evaluate the H-donating ability of H-donors or the H-accepting ability of H-acceptors in the HAT reaction. 13 The H-donating abilities of C(sp 3 )–H bonds in dihydronicotinamide adenine dinucleotide (NADH) derivatives, reductive F420 coenzyme (F420H) derivatives, activated alkanes, amines and amides (Chart 1), 13,14 O–H bonds in vitamin C/E, caffeic acid, (+)-catechin and other bioactive molecules, and phenols (Chart 2), 15 and C(sp 2 )–H bonds in aldehydes (Chart 3) 16 have been quantitatively evaluated by the thermo–kinetic parameter Δ G ≠o (XH). The H-accepting abilities of three regular types of oxygen radicals including the N–O˙ radical, C–O˙ radical, and C–O–O˙ radical and one type of nitrogen radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH˙), were investigated using Δ G ≠o (X) (Chart 4).…”

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

“…2.2 | The scale of ΔG ≠o (XH) for the studied alkanes and derivatives According to the physical meaning of ΔG ≠o (XH) discussed in previous articles, 14,[24][25][26][27][28][29][30][31] the smaller the value of ΔG ≠o (XH) is, the stronger the H-donating ability of XH in HAT reaction is. In order to more intuitively study the relationship between molecular structure and ΔG ≠o (XH), the ΔG ≠o (XH) data of different H-donors are sorted according to their values in Scheme 2.…”