Hydrogen atom abstraction groups

Selective chlorination of the 3-position of thietane 1,1-dioxide may be a consequence of hydrogen atom abstraction by a chlorine atom. Such reactions of chlorine atoms are believed to be influenced by polar effects, preferential hydrogen abstraction occurring remotely from an electron withdrawing group. The free radical chain reaction may be propagated by attack of the 3-thietanyl 1,1-dioxide radical on molecular chlorine. 

One of the most common reactions of photoexcited carbonyl groups is hydrogen-atom abstraction from solvent or some other hydrogen donor. A second common reaction is cleavage of the carbon-carbon bond adjacent to the carbonyl group ... 

Hydrogen Atom Abstraction from the C5-Methyl Group of Thymine 356... 

The rate of this intramolecular isomerization depends on the chain length, with the maximum in the case of a six-atomic transition state, i.e., when the tertiary C—H bond is in the (3-position with respect to the peroxyl group [13]. For the values of rate constants of intramolecular attack on the tertiary and secondary C—H bond, see Table 2.9. The parameters of peroxyl radical reactivity in reactions of intra- and intermolecular hydrogen atom abstraction are compared and discussed in Chapter 6. 

The generation of trimethylenemethane diyls [26] has been shown to effect DNA cleavage. Attachment of this group to a DNA binding molecule (Fig. 7) made the intramolecular hydrogen atom abstraction (DNA-drug being considered as one molecule) more efficient than the competitive dimerization of diyls. 

The kinetic data for these reactions are numerous, as shown in Table VI. Most of values were obtained by radical clock methods. The ring expansion of radical 7 has been employed as the clock in a study that provided much of the data in Table VI.74 Cyclizations of 5-hexenyl-type radicals also have been used as clocks,75-77 and other competition reactions have been used.78 Hydrogen atom abstraction from n-Bu3GeH by primary alkyl radicals containing a trimethylsilyl group in the a-, >8-, or y-position were obtained by the indirect method in competition with alkyl radical recombi-... 

Hydrogen atom abstraction from the 5-methyl group of T produces the 5-(2 -deoxyuridinyl)methyl radical (T(—H) ), which is one of the main reactive radiation-induced decomposition products of As outlined in Scheme 10,... 

The regioselectivity for the hydrogen atom abstraction from each of two geminal methyl groups (twin or twix) in trisubstituted alkenes such as 34, 35, 39 and 122 (Table 17) was studied by specific deuterium labeling. Independent studies revealed that the cis effect selectivity found in solution no longer operates within the zeolite. As seen in Table 19, for the case of 124-127, the twin methyl group reactivity increases up to 14 times (see substrate 126) by zeolite confinement. 

It was proposed that the relative reactivity of the twin and twix methyl groups for allyUc hydrogen atom abstraction within Na-Y is controlled (a) by electrostatic interactions between Na and the styrenes, and (b) by electrostatic interactions of the... 

The rate constants of a-hydrogen atom abstraction from four hydrocarbons by cumylperoxy, tetralylperoxy, and 9,10-dihdroanthracyl-9-peroxy radicals and by the normal chain-carrying peroxy radicals are compared in Table VIII. The results show that the reactivities of peroxy radicals are affected by the nature of the organic group. The relatively low propagation constant for the oxidation of pure cumene may be caused by the low reactivity of the cumylperoxy radical. 

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