Leaving group
In chemistry, a leaving group is an atom or molecule that leaves another molecule during a reaction. This reaction can be for example a nucleophilic substitution. In this case the leaving group gets a pair of electrons. Some leaving groups are better than others. This is because some atoms or molecules like getting extra electrons. The halides are a good example of good leaving groups.
The type of leaving group can change the type of reaction that happens. For example, bad leaving groups make an SN1 reaction more difficult, while they make an SN2 reaction easier.
Leaving Group Media
Common mechanistic contexts that involve the departure of a nucleofugal leaving group. The leaving group (LG) is shown in red. Top: SN2 reaction; middle/left: first step of SN1 and E1 reactions; middle/right: second step of E1cb, AAC2, and BAC2 reactions; bottom: E2 reaction.
In an ionization reaction, as in all reactions that involve leaving group departure, the leaving group bears a larger negative charge in the transition state and products than it does in the starting materials
Propyl halide toluene thiolate reaction
Ethyl halide ethoxide reaction
Leaving group activation by lewis acid complexation png
Mechanism of a general E1cB reaction
Continuum from E1cB to E2 eliminations
The ability of hyper leaving groups is enhanced by entropic factors
