Why are organic elimination reactions known as beta eliminations? Why don't we call them alpha eliminations?
$\begingroup$
$\endgroup$
2
-
$\begingroup$ 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. $\endgroup$– user55119Nov 26, 2017 at 18:25
-
$\begingroup$ Addition: ...while the C1 and C3 hydrogens are referred to as beta. $\endgroup$– user55119Nov 26, 2017 at 18:36
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
1
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.
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.
-
$\begingroup$ 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 $\endgroup$– ChemistNov 19, 2019 at 9:26