Hydrogen atom abstraction

About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.

Enantioselective radical-chain hydrosilylation of alkenes using homochiral thiols as polarity-reversal catalysts

Abstract: The thiol-catalysed radical-chain additions of triphenylsilane and of tris(trimethylsilyl)silane to a number of cyclic prochiral terminal alkenes have been carried out at 60 °C in the presence of di-tert-butyl hyponitrite as initiator. The function of the thiol catalyst is to promote the overall abstraction of hydrogen from the silane by the nucleophilic carbon-centred radical intermediate, formed by addition of the silyl radical to the alkene, and the stereogenic centre in the final adduct is set by hydrogen-atom transfer from the thiol to this β-silylalkyl radical. When the thiol is homochiral the transfer of hydrogen becomes enantioselective and an optically active adduct results. A number of homochiral thiols were investigated and the highest enantiomeric excesses (up to 95%) were achieved using the tetra-O-acetyl derivatives of 1-thio-β-D-glucopyranose and 1-thio-β-D-mannopyranose. The absolute configuration of an enantiopure triphenylsilane adduct (upgraded by recrystallisation) was determined by X-ray crystallography and it was shown that this adduct could be oxidatively desilylated to the corresponding alcohol and acetate with no loss of enantiomeric purity.

Mechanism for the Gas-Phase Reaction between Formaldehyde and Hydroperoxyl Radical. A Theoretical Study

Abstract: We present a high-level theoretical study on the gas-phase reaction between formaldehyde and hydroperoxyl radical carried out using the DFT-B3LYP, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311+G(d,p), 6-311+G(2df,2p), and aug-cc-pVTZ basis sets. The most favorable reaction path begins with the formation of a pre-reactive complex and produces the peroxy radical CH2(OO)OH in a process that is computed to be exothermic by 16.8 kcal/mol. This reaction involves a process in which the oxygen terminal of the HO2 moiety adds to the carbon of formaldehyde, and, simultaneously, the hydrogen of the hydroperoxyl group is transferred to the oxygen of the carbonyl in a proton-coupled electron-transfer mechanism. Our calculations show that this transition state lies below the sum of the energy of the reactants, and we computed a rate constant at 300 K of 9.29 × 10-14 cm3 molecule-1 s-1, which is in good agreement with the experimental results. Also of interest in combustion chemistry, we studied...

Effect of hydration on the hydrogen abstraction reaction by HO in DMS and its oxidation products.

Abstract: The gas-phase hydrogen abstraction reaction between the HO radical and sulfur containing species in the absence and presence of a single water molecule is investigated theoretically. The sulfur containing species dimethyl sulfide, dimethyl sulfoxide, and dimethyl sulfone are considered. The calculations are carried out with a mixture of density function theory and second order Moller−Plesset perturbation theory. We find that the energy of the hydrated transition state structures for the hydrogen abstraction reactions is lowered compared to that of the nonhydrated ones. Furthermore, the energy difference between the reaction complex and the transition state is reduced when one water molecule is added. The atmospheric abundance of the different hydrated complexes is estimated in order to assess the relative importance of the possible reaction mechanisms.

Acid-base chemistry in the gas phase. The cis-and trans-2-naphthol-NH3 complexes in their S0 and S1 states

Abstract: A unique view of the nascent acid‐base reaction between 2‐naphthol and ammonia along the proton transfer coordinate is provided by analyses of the rotationally resolved S1←S0 electronic spectra of their hydrogen bonded complexes cis‐ and trans‐2HNA in the gas phase. Both complexes, in both electronic states, have structures in which ammonia, acting as a base, forms an in‐plane hydrogen bond with the hydroxy hydrogen atom of 2‐naphthol. The ground state O–H⋅⋅⋅N heavy atom separations are R=2.77 A in cis‐2HNA and R=2.79 A in trans‐2HNA. Electronic excitation of the significantly more acidic S1 state of 2‐naphthol produces large decreases in R in both complexes. S1 cis‐2HNA has R=2.62 A and S1 trans‐2HNA has R=2.57 A. Comparing these results to the Lippincott–Schroeder potential for the hydrogen bond shows that there is little change in the vibrationally averaged position of the hydroxy hydrogen atom. But decreasing R produces significant decreases in the barrier to proton transfer, in the distance from reac...