Intramolecular reactions unimolecular bond formation

Radical cations exhibit a wide variety of reactions, including unimolecular reactions such as rearrangement, fragmentation, and intramolecular bond formation as well as bimolecular reactions with ionic, radical, or ground state species. Notable processes include reaction with nucleophiles to produce radicals, reaction with radicals to produce cations, reaction with electron donors to produce biradicals, and reaction with ground state molecules to give addition products. Often the products of reactions of radical cations with neutral species are different from those observed by reaction of the corresponding carbocation with the same reactant... 

As for the acetyl phosphate monoanion, a metaphosphate mechanism has also been proposed 78) for the carbamoyl phosphate monoanion 119. Once again, an intramolecular proton transfer to the carbonyl group is feasible. The dianion likewise decomposes in a unimolecular reaction but not with spontaneous formation of POf as does the acetyl phosphate dianion, but to HPOj and cyanic acid. Support for this mechanism comes from isotopic labeling proof of C—O bond cleavage and from the formation of carbamoyl azide in the presence of azide ions. 

Unimolecular radical reactions result from the instability of the first formed radical. The radicals may completely decompose or they may rearrange before reaction with other molecules or radicals present. In decomposition reactions, the radical decomposes to give a stable molecule and a new radical. In rearrangement reactions, the breaking of an adjacent C-C bond in a cyclic system leads to the concomitant formation of a new bond, usually carbonyl, and a new isomeric radical. There could also be migration of an atom, via intramolecular abstraction by the radical center, thus creating a new, isomeric radical. 

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