Reaction types
The large diversity of chemical reactions and approaches to their study results in the existence of several concurring, often overlapping, ways of classifying them. Below are examples of widely used terms for describing common kinds of reactions.
- Isomerisation, in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism
- Direct combination or synthesis, in which 2 or more chemical elements or compounds unite to form a more complex product:
- Chemical decomposition or analysis, in which a compound is decomposed into smaller compounds or elements:
- Single displacement or substitution, characterized by an element being displaced out of a compound by a more reactive element:
- Metathesis or Double displacement reaction, in which two compounds exchange ions or bonds to form different compounds:
- Acid-base reactions, broadly characterized as reactions between an acid and a base, can have different definitions depending on the acid-base concept employed. Some of the most common are:
- Arrhenius definition: Acids dissociate in water releasing H3O+ ions; bases dissociate in water releasing OH- ions.
- Brønsted-Lowry definition: Acids are proton (H+) donors; bases are proton acceptors. Includes the Arrhenius definition.
- Lewis definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.
- Redox reactions, in which changes in oxidation numbers of atoms in involved species occur. Those reactions can often be interpreted as transferences of electrons between different molecular sites or species. An example of a redox reaction is:
- 2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I−(aq)
- In which I2 is reduced to I- and S2O32- (thiosulfate anion) is oxidized to S4O62-.
- Combustion, a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used for only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.
- Disproportionation with one reactant forming two distinct products varying in oxidation state.
- 2 Sn2+ → Sn + Sn4+
Organic reactions encompass a wide assortment of reactions involving compounds which have carbon as the main element in their molecular structure. The reactions in which an organic compound may take part are largely defined by its functional groups.
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