Yamaguchi rule

In the case of double bond addition reactions, when the attacking radical approaches an alkene in the Ti-bond plane (Sect. 6.2), the Yamaguchi rule implies that a terminal attack IV is more preferable than the central (triangular) approach V ... 

Like other selection rules, the Yamaguchi rule is not absolute and by varying the structure of reactants its restrictions may be lifted. Salem and co-authors [7] have shown the conclusion as to preferability of the type I, IV approach to be fully valid only for the reaction between nonpolar reactants when covalent interactions prevail. However, in the case of zero overlap of the radical orbitals and one of the centers of the bond being attached also the triangular approach can become allowed. Such a situation may arise in reactions of radical addition to polarized alkenes that contain substituents at sp -carbon atoms. 

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