Group Increments for Radicals

The major value of free radical group increments is in the prediction of stabilities of proposed radical and biradical intermediates in various thermal and photochemical reactions. For example, we might want to determine whether an observed thermal rearrangement occurs homolytically, via biradical intermediates, or by a concerted, pericyclic process. One valuable piece of information is AH° of the proposed biradical intermediate. If it is too high for the biradical to lie on the reaction path, then the biradical route can be rejected. We will see examples of this type of analysis in Chapter 15. 

Group Increment Values for Free Radicals (kcal/mol)  

Cj = double bond Cr = benzene carbon Ni = imine nitrogen. Values in parentheses are highly approximate. 

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