Ring expansion reaction

A ring expansion reaction is a type of organic reaction in which usually a hydrocarbon ring is expanded. Examples of ring expansions are:
 * Beckmann rearrangement
 * Dowd-Beckwith ring expansion reaction.

Ring contraction reaction
A ring contraction reaction is a type of organic reaction in which usually a hydrocarbon ring is contracted

Examples are:
 * Favorskii rearrangement
 * Demjanov rearrangement
 * Ring contractions of cyclic ketones and cycloalkenes brought about by hypervalent iodine for example the reaction of cyclohexene with iodosobenzene and boron trifluoride to cyclopentanecarbaldehyde:
 * [[Image:HypervalentiodineRingContraction.png|300px|Ring contraction initiated by hypervalent iodine]]