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- Kinetic_isotope_effect abstract "Kinetic isotope effect (KIE) refers to the change in the rate of a chemical reaction upon substitution of an atom in the reactants with one of its isotopes. Formally, it is defined as the ratio of rate constants for the reactions involving the light (kL) and the heavy (kH) isotopically substituted reactants:For example, in the following nucleophilic substitution reaction of methyl bromide with cyanide, the kinetic isotope effect of the methyl carbon, in this case defined as k12/k13, was found to be 1.082 ± 0.008.Kinetic isotope effect is considered to be one of the most essential and sensitive tools for the study of reaction mechanisms, the knowledge of which allows the improvement of the desirable qualities of the corresponding reactions. For example, kinetic isotope effects can be used to reveal whether a nucleophilic substitution reaction follows a unimolecular (SN1) or bimolecular (SN2) pathway. In the case of the aforementioned reaction of methyl bromide and cyanide, the observed methyl carbon kinetic isotope effect is indicative of an SN2 mechanism. Depending on the pathway, quite different strategies may be used to stabilize the transition state of the rate-determining step of the reaction and improve the reaction rate and selectivity, which are important for industrial applications.Isotopic rate changes are most pronounced when the relative mass change is greatest, since the effect is related to vibrational frequencies of the affected bonds. For instance, changing a hydrogen atom to deuterium represents a 100% increase in mass, whereas in replacing carbon-12 with carbon-13, the mass increases by only 8%. The rate of a reaction involving a C–H bond is typically 6–10 times faster than the corresponding C–D bond, whereas a 12C reaction is only ~1.04 times faster than the corresponding 13C reaction (even though, in both cases, the isotope is one atomic mass unit heavier).Isotopic substitution can modify the rate of reaction in a variety of ways. In many cases, the rate difference can be rationalized by noting that the mass of an atom affects the vibrational frequency of the chemical bond that it forms, even if the electron configuration is nearly identical. Heavier atoms will (classically) lead to lower vibration frequencies, or, viewed quantum mechanically, will have lower zero-point energy. With a lower zero-point energy, more energy must be supplied to break the bond, resulting in a higher activation energy for bond cleavage, which in turn lowers the measured rate (see, for example, the Arrhenius equation).".
- Kinetic_isotope_effect thumbnail KIE_Lead_1.png?width=300.
- Kinetic_isotope_effect wikiPageID "1106771".
- Kinetic_isotope_effect wikiPageRevisionID "603351168".
- Kinetic_isotope_effect hasPhotoCollection Kinetic_isotope_effect.
- Kinetic_isotope_effect subject Category:Chemical_kinetics.
- Kinetic_isotope_effect subject Category:Organic_chemistry.
- Kinetic_isotope_effect subject Category:Physical_organic_chemistry.
- Kinetic_isotope_effect subject Category:Reaction_mechanisms.
- Kinetic_isotope_effect comment "Kinetic isotope effect (KIE) refers to the change in the rate of a chemical reaction upon substitution of an atom in the reactants with one of its isotopes.".
- Kinetic_isotope_effect label "Efecto isotópico cinético".
- Kinetic_isotope_effect label "Efekt izotopowy".
- Kinetic_isotope_effect label "Effet isotopique".
- Kinetic_isotope_effect label "Effetto isotopico cinetico".
- Kinetic_isotope_effect label "Isotopeneffekt".
- Kinetic_isotope_effect label "Kinetic isotope effect".
- Kinetic_isotope_effect label "Kinetisch-isotoopeffect".
- Kinetic_isotope_effect label "速度論的同位体効果".
- Kinetic_isotope_effect sameAs Isotopeneffekt.
- Kinetic_isotope_effect sameAs Efecto_isotópico_cinético.
- Kinetic_isotope_effect sameAs Effet_isotopique.
- Kinetic_isotope_effect sameAs Effetto_isotopico_cinetico.
- Kinetic_isotope_effect sameAs 速度論的同位体効果.
- Kinetic_isotope_effect sameAs Kinetisch-isotoopeffect.
- Kinetic_isotope_effect sameAs Efekt_izotopowy.
- Kinetic_isotope_effect sameAs m.046jyl.
- Kinetic_isotope_effect sameAs Q1386472.
- Kinetic_isotope_effect sameAs Q1386472.
- Kinetic_isotope_effect wasDerivedFrom Kinetic_isotope_effect?oldid=603351168.
- Kinetic_isotope_effect depiction KIE_Lead_1.png.
- Kinetic_isotope_effect isPrimaryTopicOf Kinetic_isotope_effect.