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The kinetic isotope effect (KIE) is a variation in the reaction rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. It is also called isotope fractionation, although this term is technically somewhat broader in meaning. A KIE involving hydrogen and deuterium is represented as: The rusting of iron. ...
A chemical reaction occurs when vapours of hydrogen chloride and ammonia meet to form a cloud of a new substance, ammonium chloride Chemical reaction is a process that results in the interconversion of chemical substances [1]. The substance or substances initially involved in a chemical reaction are called reactants. ...
Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle of a chemical element that retains its chemical properties. ...
Isotopes are any of the several different forms of an element each having different atomic mass. ...
General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...
Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of planet Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ...
with kH and kD reaction rate constants. In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction. ...
An isotopic substitution will greatly modify the reaction rate when the isotopic replacement is in a chemical bond that is broken or formed. In such a case, the rate change is termed a primary isotope effect. When the substitution is not involved in the bond that is breaking or forming, one may still observe a smaller rate change, termed a secondary isotope effect. Thus, the magnitude of the kinetic isotope effect can be used to elucidate the reaction mechanism. Isotope effects are most easily observed when they occur in the rate-determining step of a reaction. If other steps are partially rate-determining, the effect of isotopic substitution will be masked. The rusting of iron. ...
A chemical bond is the physical phenomenon (or phenomena) responsible for the attractive interactions between atoms that confers stability to di- and polyatomic chemical compounds. ...
In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. ...
The rate-determining step is a chemistry term for the slowest step in a chemical reaction. ...
Isotopic rate changes are most pronounced when the relative mass change is greatest. 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 to 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). Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ...
General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...
Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of planet Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ...
General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ...
The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. ...
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 vibration 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). Sine waves of various frequencies; the bottom waves have higher frequencies than those above. ...
A chemical bond is the physical phenomenon (or phenomena) responsible for the attractive interactions between atoms that confers stability to di- and polyatomic chemical compounds. ...
The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...
Classical physics is physics based on principles developed before the rise of quantum theory, usually including the special theory of relativity and general theory of relativity. ...
Fig. ...
In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess; it is the energy of the ground state of the system. ...
The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ...
The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of a chemical reaction rate. ...
The Swain equation relates the kinetic isotope effect for the proton/tritium combination with that of the proton/deuterium combination. The Swain equation relates the kinetic isotope effect for the proton/tritium combination with that of the proton/deuterium combination according to: where kH,D,T is the reaction rate constant for the protonated, deuterated and tritiated reactants. ...
Mathematical details in a diatomic molecule
One approach to studying the effect is for that of a diatomic molecule. The fundamental vibrational frequency (ν) of a chemical bond between atom A and B is, when approximated by a harmonic oscillator: In classical mechanics, a Harmonic oscillator is a system which, when displaced from its equilibrium position, experiences a restoring force proportional to the displacement according to Hookes law: where is a positive constant. ...
where k is the spring constant for the bond, and μ is the reduced mass of the A-B system: Reduced mass is an algebraic term of the form that simplifies an equation of the form The reduced mass is typically used as a relationship between two system elements in parallel, such as resistors; whether these be in the electrical, thermal, hydraulic, or mechanical domains. ...
(mi is the mass of atom i). Quantum mechanically, the energy of the n-th level of a harmonic oscillator is given by: Thus, the zero-point energy (n = 0) will decrease as the reduced mass increases. With a lower zero-point energy, more energy is needed to overcome the activation energy for bond cleavage.
In changing a carbon-hydrogen bond to a carbon-deuterium bond, k remains unchanged, but the reduced mass µ is different. As a good approximation, on going from C-H to C-D, the reduced mass increases by a factor of approximately 2. Thus, the frequency for a C-D bond should be approximately 1/√2 or 0.71 times that of the corresponding C-H bond. Still, this is a much larger effect than changing the carbon-12 to carbon-13.
Applications The kinetic isotope effect is applied in reaction mechanism elucidation, for instance in the halogenation of toluene [1]: In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. ...
In chemistry, halogenation is a chemical reaction that replaces a hydrogen atom with a halogen atom. ...
Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, reminiscent of the sweet smell of the related compound benzene. ...
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 In this particular intramolecular KIE study the radical substitution of hydrogen by bromine is examined with mono-deuterated toluene (obtained by organic reduction of benzyl chloride with zinc and deuterated acetic acid) and N-bromosuccinimide. As hydrogen is replaced by bromine faster than deuterium, the reaction product gets enriched in deuterium. In order to analyze the deuterium composition by means of mass spectroscopy the reaction product is reduced back to toluene with lithium aluminum hydride and a KIE of 4.86 is calculated. This finding is in accordance with the general accepted view of a radical substitution in which in the rate-determining step a proton is removed by a bromine free radical species. Image File history File links Download high-resolution version (946x592, 8 KB) (Delete all revisions of this file) (cur) 01:14, 22 August 2006 . ...
In Organic chemistry, a radical substitution reaction is a substitution reaction where a radical is the intermediate and the product is an alkyl halide. ...
Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. ...
Benzyl chloride, or α-chlorotoluene, is an organic compound consisting of a benzene ring substituted with a chloromethyl group. ...
General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ...
Acetic acid, also known as ethanoic acid, is an organic chemical compound best recognized for giving vinegar its sour taste and pungent smell. ...
Flash point None R/S statement R: ? S: ? RTECS number ? Supplementary data page Structure and properties n, εr, etc. ...
Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ...
Lithium aluminum hydride (LiAlH4, commonly abbreviated to LAH) is a powerful reducing agent used in organic chemistry. ...
The rate-determining step is a chemistry term for the slowest step in a chemical reaction. ...
In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ...
A large KIE of 5.56 is also reported for reaction of ketones with bromine and sodium hydroxide forming a haloketone with the α-carbonyl positions deuterated [2]. Ketone group A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a chemical compound that contains this functional group. ...
General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ...
Sodium hydroxide (NaOH), also known as lye or caustic soda, is a caustic metallic base. ...
A haloketone in organic chemistry is a functional group consisting of a ketone group with a α-halogen substituent. ...
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 In this reaction the rate-limiting step is enolate formation by proton (deuterium) abstraction from the ketone by base. In this study the KIE is calculated from the reaction rate constants for regular 2,4-dimethyl-3-pentone and its deuterated isomer by optical density measurements. Image File history File links Download high-resolution version (1063x455, 8 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Kinetic isotope effect ...
Enol (or, more officially, but less commonly: alkenol) is an alkene with hydroxyl group on one of the carbon atoms of the double bond. ...
In chemical kinetics a reaction rate constant quantifies the speed of a chemical reaction. ...
Optical density is the absorbance of an optical element for a given wavelength λ per unit distance: Where: = the distance that light travels through the sample (i. ...
Tunneling In some cases, an additional rate enhancement is seen for the lighter isotope, possibly due to quantum mechanical tunnelling. This is typically only observed for hydrogen atoms, which are light enough to exhibit significant tunnelling. Quantum tunnelling (or tunneling) is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...
This effect has been observed in such reactions as the deprotonation and iodination of nitropropane with hindered pyridine base [3] with a reported KIE of 25 at 25°C: Deprotonation is a chemistry term that refers to the removal of a proton (hydrogen ion H+) from a molecule, forming the conjugate base. ...
Nitro compounds are organic compounds that contain one or more nitro functional groups (-NO2). ...
Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively sour odour. ...
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 and in a 1,5-sigmatropic hydrogen shift [4] although it is observed that it is difficult to extrapolate experimental values obtained at elevated temperatures to lower temperatures [5] [6]: Image File history File links Download high-resolution version (1048x354, 6 KB) KIE_effect_iodination Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ...
A Sigmatropic reaction is a pericyclic reaction where the net result is one sigma bond being changed to another sigma bond. ...
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 Image File history File links Download high-resolution version (991x330, 7 KB) KIE_effect_sigmatropic Reaction I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ...
See also Barton Hawkins, also known as Barton K. Hawkins (1961 - ) instigated several key advances in biochemistry and biophysics, most notably his invention of the intramolecular kinetic isotope effect. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
In physical chemistry, chemical kinetics or reaction kinetics study reaction rates in a chemical reaction. ...
External links - Testing a Mechanism: Kinetic Isotope Effects
- Primary Kinetic Isotope Effect
- Measuring Kinetic Isotope Effect of Carbon at Natural Abundance
- Kinetic Isotope Effects in Barrierless Reactions of CH Radicals
- Singleton Research Group
- Kinetic Isotope Effects in the Hydride Transfer Reaction of Xylose Isomerase
- Stable chlorine intramolecular kinetic isotope effects from the abiotic dehydrochlorination of DDT
References - ^ The Deuterium Isotope Effect in the Side Chain Halogenation of Toluene Kenneth B. Wiberg and Lynn H. Slaugh J. Am. Chem. Soc.; 1958; 80(12) pp 3033 - 3039; DOI:10.1021/ja01545a034 10.1021/ja01545a034
- ^ Anomalous kinetic hydrogen isotope effects on the rat of ionization of some dialkyl substituted ketones R. A. Lynch, S. P. Vincenti, Y. T. Lin, L. D. Smucker, and S. C. Subba Rao J. Am. Chem. Soc.; 1972 94pp 8351 - 8356; DOI:10.1021/ja00779a012 10.1021/ja00779a012
- ^ Rates and isotope effects in the proton transfers from 2-nitropropane to pyridine bases Edward Sheldon Lewis and Lance Funderburk J. Am. Chem. Soc.; 1967; 89(10) pp 2322 - 2327; DOI:10.1021/ja00986a013
- ^ Mechanism of the 1,5-sigmatropic hydrogen shift in 1,3-pentadiene Michael J. S. Dewar, Eamonn F. Healy, and James M. Ruiz J. Am. Chem. Soc.; 1988; 110(8) pp 2666 - 2667; DOI:10.1021/ja00216a060
- ^ Effect on Kinetics by Deuterium in the 1,5-Hydrogen Shift of a Cisoid-Locked 1,3(Z)-Pentadiene, 2-Methyl-10-methylenebicyclo[4.4.0]dec-1-ene: Evidence for Tunneling? William von E. Doering and Xin Zhao J. Am. Chem. Soc.; 2006; 128(28) pp 9080 - 9085; (Article) DOI:10.1021/ja057377v
- ^ In this study the KIE is measured by sensitive proton NMR. The extrapolated KIE at 25°C is 16.6 but the margin of error is high
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