Leaving group
Leaving Group
A Leaving Group (pronounced: lee-ving groop) is a term used in organic chemistry to describe a molecular fragment that departs with a pair of electrons in heterolytic bond cleavage. Leaving groups can be anions or neutral molecules, but in either case, it is crucial that they are stable on their own, as they will exist as a separate entity after the bond breaks.
Etymology
The term "Leaving Group" is derived from the English words "leaving", meaning to go away from a place, and "group", referring to a number of people or things that are located, gathered, or classed together. In the context of organic chemistry, it refers to a group of atoms that leaves the molecule during a chemical reaction.
Related Terms
- Nucleophile: A chemical species that donates an electron pair to form a chemical bond in relation to a reaction.
- Electrophile: A reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.
- Substitution Reaction: A chemical reaction during which one functional group in a chemical compound is replaced by another group.
- Elimination Reaction: A type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism.
Leaving Group Ability
The ability of a leaving group to depart from its parent molecule is measured by the ease with which it can accept a pair of electrons. This is often related to the basicity of the leaving group; the weaker the base, the better the leaving group. Common leaving groups include halides such as Cl-, Br-, and I-, as well as water and sulfonate esters.
Leaving Group in Substitution and Elimination Reactions
In both substitution reactions and elimination reactions, the role of the leaving group is crucial. It leaves the parent molecule, allowing a new bond to form in substitution reactions, or a pi bond to form in elimination reactions.
External links
- Medical encyclopedia article on Leaving group
- Wikipedia's article - Leaving group
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