Relative reactivity of alkenes toward halogenation

Little can be said about the mechanisms of fluorination or iodination of alkenes by the molecular halogens. Fluorine reacts violently with alkenes, giving mixtures including products resulting from degradation of the carbon chain. There have been few mechanistic studies of the reaction with iodine. One significant feature of the reaction is its reversibility. Some iodine remains in equilibrium with simple alkenes. 

The addition is stereospecifically anti. It is not entirely clear whether a polar mechanism is involved. A radical chain mechanism has been proposed.  

There are many other reactions that involve electrophilic addition to carbon-carbon double bonds. In some cases, such as mercuration, there have been extensive mechanistic studies. We will, however, defer discussion of these reactions to Part B, Chapter 3, where their synthetic utility can also be emphasized. 

An elimination reaction—the expulsion of a small molecule from an organic substrate—can be classified according to the relative placement of the carbon atoms from which elimination occurs  

The jS-eliminations can be further subdivided by closer examination df the mechanisms involved. The three distinct mechanisms that can operate in such reactions are outlined below  

---

Table 6.3. Relative Reactivity of Alkenes toward Halogenation...

---