Reaction intermediate
molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction
In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding intermediates, but is consumed in a later step. It does not appear in the chemical equation for the overall reaction. For example, consider this hypothetical reaction:
A + B → C + D
If this overall reaction comprises two elementary steps thus:
A + B → X
X → C + D
then X is a reaction intermediate.
The phrase reaction intermediate is often abbreviated to the single word intermediate, and this is IUPAC's preferred form of the term.
In most non-biological cases, a reaction intermediate is also a reactive intermediate: a short-lived, high-energy species too reactive for isolation. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. low temperatures, matrix isolation. Instead, reactive intermediates are only observable through fast spectroscopic methods.
This brief starts where responsible research should: with the source description of “Reaction intermediate” as molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the science & nature register because the source frames it as molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Datasets, specimens, observations and peer-reviewed methods provide the appropriate test for the technical claims summarized here. The source revision retrieved here is dated Sep 14, 2026. The linked authority identifier is Q7458208. The Library of Congress control number is sh92001557. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
Scientific names, classifications and consensus can change while older terminology persists in catalogues and historical literature. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Reaction intermediate” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.