Elimination reaction

In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists.

E1 stands for unimolecular elimination and has the following specifications An example in scheme 2 is the reaction of tert-butylbromide with potassium ethoxide in ethanol.

Specific features : The reaction rate is influenced by the reactivity of halogens, iodide and bromide being favored.

In general, with the exception of reactions in which E2 is impossible because β hydrogens are unavailable (e.g. methyl, allyl, and benzyl halides),[4] clean SN2 substitution is hard to achieve when strong bases are used, as alkene products arising from elimination are almost always observed to some degree.

[5] In one study[6] the kinetic isotope effect (KIE) was determined for the gas phase reaction of several alkyl halides with the chlorate ion.

The ability to form a stable product containing a C=C or C=X bond, as well as orbital alignment considerations, strongly favors β-elimination over other elimination processes.

For instance, α-elimination the elements of HCl from chloroform (CHCl3) in the presence of strong base is a classic approach for the generation of dichlorocarbene, :CCl2, as a reactive intermediate.

(Confusingly, in organometallic terminology, the terms α-elimination and α-abstraction refer to processes that result in formation of a metal-carbene complex.

In certain special cases, γ- and higher eliminations to form three-membered or larger rings is also possible in both organic and organometallic processes.