Selectivity Semenov

It is follows from Equations (6.23) and (6.24) that the coefficient a in the Polany-Semenov equation depends not only on parameters Are and a but also on the incidental factor such as the range of variation of enthalpies of the selected series of reactions. The same situation is observed for coefficient p in the Hammett and Taft equations (see Equation [6.2]) [11],... 

To illustrate these Semenov diagrams in reasonable quantitative terms, n-heptane was selected with the following properties ... 

This mode of initiation was first suggested by Cullis and Hinshelwood [5] and substantiated theoretically by Semenov [34]. The activation energies of such abstraction reactions are ca. 40—55 kcal. mole and reflect their high endothermicity. They are therefore slow and selective and as would be expected from the C—H bond strengths, tertiary C—H bonds are the most readily attacked and primary C—H bonds the least readily attacked. 

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