- 関
- dyad、dyadic
WordNet
- relating to or affecting two molecules
- of or relating to a dyad or based on two
Wikipedia preview
出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/02/04 11:05:49」(JST)
[Wiki en表示]
Molecularity in chemistry is the number of colliding molecular entities that are involved in a single reaction step.[1] While the order of a reaction is derived experimentally, the molecularity is a theoretical concept and can only be applied to elementary reactions. In elementary reactions, the reaction order, the molecularity and the stoichiometric coefficient are the same, although only numerically, because they are different concepts.
- A reaction involving one molecular entity is called unimolecular.
- A reaction involving two molecular entities is called bimolecular.
- A reaction involving three molecular entities is called termolecular. Termolecular reactions in solutions or gas mixtures are very rare, because of the improbability of three molecular entities simultaneously colliding.[2] However the term termolecular is also used to refer to three body association reactions of the type:
Where the M over the arrow denotes that to conserve energy and momentum a second reaction with a third body is required. After the initial bimolecular collision of A and B an energetically excited reaction intermediate is formed, then, it collides with a M body, in a second bimolecular reaction, transferring the excess energy to it.[3]
The reaction can be explained as two consecutive reactions:
These reactions frequently have a pressure and temperature dependence region of transition between second and third order kinetics.[4]
Catalytic reactions are often three-component, but in practice a complex of the starting materials is first formed and the rate-determining step is the reaction of this complex into products, not an adventitious collision between the two species and the catalyst. For example, in hydrogenation with a metal catalyst, molecular dihydrogen first dissociates onto the metal surface into hydrogen atoms bound to the surface, and it is these monatomic hydrogens that react with the starting material, also previously adsorbed onto the surface.
Notes and references
- ^ Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "molecularity". IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.{{{file}}}. ISBN 0-9678550-9-8. http://goldbook.iupac.org/M03989.html.
- ^ Discussion on the improbability of termolecular reactions
- ^ Text discussing rate constants for termolecular reactions [1]
- ^ IUPAC definition of Troe expression, a semiempirical expression for the rate constant of termolecular reactions [2]
See also
- Reaction rate
- Order of reaction
Basic reaction mechanisms
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Nucleophilic substitutions |
- Unimolecular nucleophilic substitution (SN1)
- Bimolecular nucleophilic substitution (SN2)
- Nucleophilic aromatic substitution (SNAr)
- Nucleophilic internal substitution (SNi)
- Nucleophilic acyl substitution
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Elimination reactions |
- Unimolecular elimination (E1)
- E1cB elimination reaction
- Bimolecular elimination (E2)
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|
Addition reactions |
- Electrophilic addition
- Nucleophilic addition
- Free-radical addition
- Cycloaddition
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|
Related topics |
- Elementary reaction
- Molecularity
- Stereochemistry
- Catalysis
- Collision theory
- Solvent effects
- Arrow pushing
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Chemical kinetics |
- Rate equation
- Rate-determining step
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|
UpToDate Contents
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Related Links
- A reaction involving two molecular entities is called bimolecular. ... After the initial bimolecular collision of A and B an energetically excited reaction intermediate is formed, then, it collides with a M body, in a second bimolecular reaction, ...
- Also found in: Encyclopedia, Wikipedia, 0.01 sec. bi·mo·lec·u·lar (b m -l k y -l r). adj. Relating to, consisting of, or affecting two molecules. bi mo·lec u·lar·ly adv. bimolecular [ˌbaɪməˈlɛkjʊlə]. adj. (Chemistry) (of a chemical complex, collision, ...
★リンクテーブル★
[★]
- 関
- bimolecular、dyad
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- 英
- dyad、bimolecular、dyadic
- 関
- 二分染色体
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- 関
- See also Lipid bilayer