What is typically true of leaving groups in a reaction?

In a chemical reaction, leaving groups are typically entities that depart from the substrate during the course of a reaction, such as a nucleophilic substitution or elimination reaction. The nature of a good leaving group is closely related to its stability when it is released from the molecule, and this stability is often decreased for stronger bases.

Weak bases are more likely to be good leaving groups because they can stabilize the negative charge that forms when they are expelled from the substrate. For example, halides like chloride (Cl⁻) and bromide (Br⁻) are considered good leaving groups because they are weak bases. When they leave, they do not significantly destabilize the intermediate or the final product, allowing the reaction to proceed smoothly.

In contrast, strong bases, like hydroxide (OH⁻) or alkoxides, are generally poor leaving groups because when they are released, they tend to form very reactive species that are unstable, making it less favorable for the reaction to occur.

Neutral species can be leaving groups, but they do not fit the typical criteria for "good" leaving groups as defined by their ability to stabilize the charge when they leave.

Lewis acids, while often able to accept electrons and play vital roles in various mechanisms, are not