siteradicals

Siteradicals are a conceptual tool used in organic chemistry to describe hypothetical reactive intermediates. They represent a fragment of a molecule where a bond has been cleaved, leaving unpaired electrons or formal charges on specific atoms. Unlike true radicals which involve an unpaired electron, siteradicals can also encompass species with carbocations, carbanions, or even biradicals. The term "siteradical" emphasizes the location or "site" within a molecule where such a reactive species might exist, often as a transient precursor to a more stable product.

These hypothetical intermediates are useful for mechanistic investigations, allowing chemists to propose plausible pathways for chemical reactions. By considering the formation and subsequent reactions of siteradicals, one can rationalize observed product distributions and understand the energetic profiles of transformations. For example, in the study of carbocation rearrangements, a carbocation intermediate can be viewed as a siteradical with a positive charge on a specific carbon atom. Similarly, in reactions involving nucleophilic attack on an electrophilic center, a transient species with a developing negative charge could be considered a siteradical. The concept is particularly relevant in homolytic, heterolytic, and even concerted reaction mechanisms where bond breaking and formation occur.