Hydrogen atom abstraction channel

In summary, we have demonstrated that photolysis/fluores-cence chemical kinetics techniques must exploit ongoing advances in laser technology. A highly-sensitive, quasi-cw, ultraviolet laser source was constructed and used in definitive chemical kinetics experiments. OH-ethylene reactions have been characterized in terms of OH addition and hydrogen atom abstraction channels, and questions have been raised concerning both the importance of the addition process and the accuracy of presently recommended kinetic parameters for the abstraction process at combustion temperatures. 

There are two channels of the reaction of acylperoxyl radicals with olefins hydrogen atom abstraction and addition to the double bond with epoxide formation [5,35] ... 

Reactions of the ground state, NH (X X ), play an important role in combustion processes. Triplet NH reacts with molecular hydrogen, water and CO2. Modem theoretical study demonstrates that reactions with H2 and H2O proceed via hydrogen atom abstraction. The NH abstracts hydrogen atoms from starting material, hydrazoic acid, and from hydrocarbons to form aminyl (NH2 ) and aUcyl radicals in spite of the fact that some reactions are endothermic, depending on the alkane. Absolute rate constants for many of these reactions have been measured in the gas phase. Triplet NH also reacts with aUcenes via formation of an intermediate triplet diradical which then decomposes into several reaction channels. ... 

Lahav, Leiserowitz and their coworkers have used inclusion complexes of deoxycholic acid to carry out asymmetric photochemical reactions. The authors reported that acetophenone forms a 2 5 crystalline channel inclusion complex with deoxycholic acid 22 as the host and that irradiation of the complex in th4 solid state leads to abstraction of a hydrogen atom by the acetophenone 23a from C5 of the steroid followed by coupling of the resulting radical pair to produce1 photoproduct 24 (Scheme 9) [216,219]. The authors were able to follow the course of the reaction by x-ray crystallography. Only one diastereomer of the product was obtained in the reaction. Aoyama et al. have studied the reaction of AT,N-dialkylpyruvamides in deoxycholic acid inclusion crystals (Scheme 10) [246], Solid-state irradiation of the inclusion complex of 22 and 25 gave the... 

The potential energy surface of hydrogen absfracfions during the reaction of n-bromopropane with OH radicals and Cl atoms is explored in detail. 1-Bromopro-pane contains three different reactive sites from where hydrogen atoms can be abstracted a, /3, and y carbon atoms. The a carbon (primary) atom is defined as the carbon to which the substituent, in this case the bromine atom, is attached. The adjacent carbon atom is called the /3-carbon. The three resulting reaction channels proceed as follows, where X = OH/Cl,... 

We report in Table 1 the theiinodynarnies of the most important reaction channels that are open under LEO conditions. Abstraction of a hydrogen atom to generate OH and alkyl radicals is the reaction pathway that has been observed in... 

The reactions of F( P) atoms have been studied kinetically in a discharge-flow apparatus at 297 K. The major reaction channel for the F-hICl reaction forms IF + Cl, although a minor process yields CIF + I. Fluorine atoms react with CO and Xe slowly to yield COF2 and XeFj, respectively, but no reaction was detected with either He or Kr. Fluorine atoms abstracted hydrogen from HOF, generating OF radicals. The mechanisms of the reactions of F and OF radicals with NOF have been investigated by Schumacher et al. Quantum yields were shown to be... 

NH in its lowest singlet state (a A) inserts readily into paraffin CH bonds. In this electronic state the nitrene also abstracts hydrogen atoms from hydrocarbons and undergoes quenching to the ground triplet state. For example, the ratio of these channels is 0.6 0.1 03 in the case of the reaction of NH with ethane ... 

Calculation of the reaction paths for both reactions (6) and (7) have been reported by Harding Wagner (38). These calculations employed a polarized double zeta basis set and a four orbital - four electron CASSCF wavefunction. This wavefunction allows for the correlation of both CH bond pairs of formaldehyde and thus provides a qualitatively correct description of both reaction pathways. The angular dependence of the potential surface for a hydrogen atom moving in the field of a frozen formyl radical is shown in Figure 6. Two reactive channels are clearly seen in this plot. One, on the left side of the plot, leads to the addition product, formaldehyde, while the other, on the right side of the plot, leads directly to abstraction products, H2 + CO. From this plot it can be seen that there is no barrier for either reaction. 

The H2 + OH H -I- H2O reaction is a prototype reaction for H atom abstraction by an OH radical to form water as a product. Moreover, it is important in combustion chemistry and interstellar chemistry [85,142]. Consequently, it has attracted extensive experimental and theoretical studies. Crossed-molecular beam experiments on the isotopically substituted D2-I-OH D- -HOD reaction revealed that the product was strongly backward-scattered, with the majority of the available energy channeled into HOD internal excitation and the newly formed OD bond in the HOD molecule preferentially excited to the v = 2 state [123]. The reverse reaction has also been studied widely as a prototype system for mode specific chemistry, in which different vibrational modes in the reactants can play an important role in the reaction dynamic. As three of the four atoms in this system are hydrogen isotopes, it has been straightforward to pursue both high-quality ab initio calculation of a PES and accurate quantum dynamics calculations. As a result, this reaction has become a benchmark system for four-atom reactions, in much the same role that the H -I- H2 reaction played for three-atom reactions. 

---