Illustrated Glossary of Organic Chemistry

β-Elimination (beta-elimination): A chemical reaction in which atoms or groups are lost from adjacent atoms, resulting in a new pi bond: A-B-C-D ---> A + B=C + D. One of atoms lost is usually (but not always) a proton. The new pi bond is usually (but not always) formed between two carbon atoms.

		+
	2-Methyl-2-butene Trisubstituted internal alkene Major product		2-Methyl-1-butene Disubstituted terminal alkene Minor product

Beta-elimination of an alkyl bromide with methoxide ion (a strong base) forms an alkene via the E2 mechanism. The reaction follows Zaitsev's rule, giving the more highly substituted alkene as the major product.


Beta-elimination of a vinyl bromide using sodamide (NaNH₂; (a strong base) as the base forms an alkyne.