Reaction intermediate

A short-lived chemical species formed in one step of a multistep reaction and consumed in a later step. It lies on the reaction pathway but is not a starting material or final product.

Reaction mechanism: A step-by-step account of how reactants are transformed into products through bond breaking and formation. Intermediates are the species that appear and disappear along a multistep mechanism.
Chemical species: A chemically distinct form of matter, defined by composition, structure, charge, or electronic state. An intermediate is a species distinguished by its place within a reaction sequence.
Carbocation: An organic ion in which a carbon atom bears a positive charge and has only six valence electrons. Carbocations are common intermediates in substitution, elimination, and rearrangement reactions.
Flash photolysis: A technique that uses a brief light pulse to generate reactive species and monitor their subsequent reactions. It can create and track short-lived intermediates on rapid timescales.
Concerted reaction: A reaction in which bond changes occur in one elementary step without a discrete intermediate. A concerted pathway has no intermediate between reactants and products.
Transition state: A highest-energy configuration along a reaction pathway, characterized by partial changes in bonding. Unlike an intermediate, a transition state is not a species at a local energy minimum.
Chemical reaction: A process in which substances are converted into other substances through rearrangement of atoms and electrons. Intermediates arise when a reaction proceeds through more than one elementary step.
Carbanion: An organic ion in which a carbon atom bears a negative charge and a lone pair of electrons. Carbanions act as intermediates in reactions that form carbon–carbon bonds.
Stopped-flow method: A rapid-mixing technique that measures reactions shortly after reactants are combined. It follows intermediates that accumulate during fast solution reactions.
Reaction intermediate versus transition state: A comparison of stable-enough pathway species with the higher-energy configurations connecting them. The distinction separates local energy minima from fleeting passage points in a mechanism.

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