Beta-elimination, also called 1,2-elimination, removes groups from adjacent atoms while forming a new multiple bond between those atoms. The IUPAC definition allows the two central atoms to be elements other than carbon, although carbon–carbon examples are common. It describes the overall connectivity change, rather than specifying one unique reaction mechanism.[ref]
The net dehydration of ethanol illustrates the topology:One carbon loses a hydrogen and its neighbor loses the oxygen-containing group; the carbon pair becomes the double bond of ethene. Both sides contain two carbons, six hydrogens and one oxygen. The balanced equation describes the net conversion, without asserting that unactivated ethanol changes spontaneously or that all bond changes occur in one step.
The positional label beta must be separated from the mechanistic label in E2 elimination. Both an E1 elimination and an E2 elimination can produce a beta-elimination transformation. Their differing intermediates, rate laws and geometric requirements are further information beyond the atom-connectivity pattern.
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