Leaving group

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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.

In this SN2 reaction, bromide (Br) is the leaving group and hydroxide (OH) is the nucleophile.

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.