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.

Ab Initio Mechanism and Multichannel RRKM−TST Rate Constant for the Reaction of Cl(2P) with CH2CO (Ketene)

Abstract: The potential energy surface for the most important pathways of the reaction between Cl(2P) and ketene has been studied using the ab initio G2(MP2) method. A variety of possible complexes and saddle points along the minimum energy reaction paths have been characterized at the UMP2(full)/6-31G(d,p) level. The calculations reveal that the addition−elimination mechanism dominates the Cl + CH2CO reaction and the direct hydrogen abstraction pathway is negligible. It is interesting to note that the addition reaction starts by the formation of a p−π complex (PπC), and subsequently the chlorinated acetyl radical CH2ClCO(2A‘) and the chloroformyl methyl radical CH2CClO(2A‘ ‘) are formed through the isomerization of PπC. The C−C bond scission of CH2ClCO(2A‘) leads to the products CO and CH2Cl. The three-center HCl elimination from PπC, occurring via a high energy barrier (TS3) and a weakly bound hydrogen bonding (HBC1), was proposed to account for the minor yield of the HCl + HCCO observed experimentally. Multichan...

1,5- and 1,9-Hydrogen atom abstractions. Photochemical strategies for radical cyclizations

Abstract: In the context of developing new radical cyclization methods, we examined the interception of the biradicals produced by the photolysis of α-keto esters.

Reaction and complex formation between OH radical and acetone

Abstract: Kinetics and mechanism of the reaction of OH with CH3C(O)CH3 have been studied by discharge-flow experiments and CCSD(T) quantum chemical computations. In the experiments, the rate coefficient for the overall reaction, OH + CH3C(O)CH3 → products (1), and the branching ratio for the specific reaction channel OH + CH3C(O)CH3 → CH2C(O)CH3 + H2O (1a) have been determined to be k1 = (1.04 ± 0.03) × 1011 cm3 mol−1 s−1 and Γ1a = k1a/k1 = 0.50 ± 0.04, respectively (T = 298 K). Two different reaction pathways have been characterized by ab initio calculations. Both H atom abstraction and OH addition to the CO group have been found to occur through hydrogen bonded OH···CH3C(O)CH3 complexes. Most of our results support recent findings (M. Wollenhaupt, S. A. Carl, A. Horowitz and J. N. Crowley, J. Phys. Chem. A, 2000, 104, 2695; M. Wollenhaupt and J. N. Crowley, J. Phys. Chem. A, 2000, 104, 6429) but contradictions remain concerning the mechanism of this atmospherically important reaction.

Temperature dependence of diffusion of radical intermediates probed by the transient grating method

Abstract: Diffusion processes of intermediate radicals created by the photoinduced hydrogen abstraction reactions of ketones, quinones, and N‐hetero aromatic molecules in ethanol and 2‐propanol are studied at various temperatures by using the transient grating (TG) method. The temperature dependences of the translational diffusion coefficients (D’s) of both the radicals and the parent molecules can be expressed by the Arrhenius relationship. The activation energies (ED) for diffusion of the radicals are larger than those of the parent molecules and the difference in ED depends on the molecular size. The different ED is explained in terms of the molecular volume dependence of ED; that is, larger molecular volumes of the radicals could be the cause of the larger ED. The larger apparent molecular volumes of the radicals are consistent with a model of microscopic aggregation of the surrounding molecules around the radical.