VI. Summary

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Intramolecular hydrogen-atom abstraction often involves reaction of an oxygen-centered radical. Since the most stable transition state for internal hydrogen-atom transfer nearly always has a six-membered ring, the 1,5-hydrogen migration (1,5-radical translocation) that occurs is a highly regioselective reaction. Only the most reactive carbon-centered radicals (vinylic and primary) consistently are able to abstract hydrogen atoms from carbon–hydrogen bonds. Such abstraction usually is an intramolecular reaction.

Site selectivity occurs in reactions of compounds with groups and atoms other than hydrogen, but such reactions are rare because few carbohydrates contain two or more of the same reactive groups (or atoms). Compounds with two of the same O-thiocarbonyl groups or two isocyano groups are known to react selectively with the tri-n-butyltin radical. In such reactions significant selectivity exists if there is a choice between forming a primary or a secondary radical.