Concept
Reaction mechanism
Overview
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical reaction occurs.
A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each.
The electron or arrow pushing method is often used in illustrating a reaction mechanism; for example, see the illustrations of the mechanisms for Michael addition and benzoin condensation in the following examples section.
Mechanisms also are of interest in inorganic chemistry. An often quoted mechanistic experiment involved the reaction of the labile hexaaquo chromous reductant with the exchange inert pentammine cobalt(III) chloride.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
Possible passages
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What is called chemical analysis is the process of searching for the causes of a phenomenon among its effects, or rather among the effects produced by the action of some other causes upon it.
John Stuart Mill, A System of Logic, Ratiocinative and Inductive
States what Reaction mechanism is.
For purposes of general consideration, however, it is only the _entire_ state which, by bringing about its successor, can be regarded as the cause. The single requisites which, added together, complete and constitute the cause may be called causal elements (_ursächliche Momente_) or even _conditions_, and into these accordingly the cause may be subdivided. On the other hand, it is quite wrong to call the objects…
Arthur Schopenhauer, On the Fourfold Root of the Principle of Sufficient Reason, and On the Will in Nature
States what Reaction mechanism is.
Where action (consequently activity and force) exists, substance also must exist, and in it alone must be sought the seat of that fruitful source of phenomena. Very well. But if we are called upon to explain what we mean by substance, and wish to avoid the vice of reasoning in a circle, the answer is by no means so easy. How shall we conclude immediately from the action to the permanence of that which acts, this…
Immanuel Kant, The Critique of Pure Reason
States what Reaction mechanism is.
Related ideas
Place in the tradition
Part of Philosophy of science.