Why are organic elimination reactions known as beta eliminations? Why don't we call them alpha eliminations?

  • $\begingroup$ Take 2-bromobutane as an example. The C2 hydrogen is an alpha carbon while the hydrogens are referred to as beta. C4-H's are gamma. It is a generic terminology that fits all cases regardless of the numbering in the compound. There are alpha and beta eliminations. $\endgroup$ – user55119 Nov 26 '17 at 18:25
  • $\begingroup$ Addition: ...while the C1 and C3 hydrogens are referred to as beta. $\endgroup$ – user55119 Nov 26 '17 at 18:36

In an elimination reaction we typically have a leaving group (denoted by "X" in the figure below), The carbon that the leaving group is attached to is referred to as the "alpha" carbon. If a hydrogen is removed from the "beta" carbon, then we have formed an olefin and the reaction is called a beta elimination.

The alpha and beta carbons in an elimination reaction


Sometimes an alpha hydrogen can be removed. In this case both the hydrogen and leaving group were attached to the same carbon and a carbene is formed.

alpha elimination

  • $\begingroup$ It would be helpful if you would add to your answer, As to why base (K OH +alc) attacks beta hydrogen and not alpha hydrogen $\endgroup$ – Chemist Nov 19 '19 at 9:26

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