Secondary hydrogen isotope effect in the unimolecular decomposition of 2-methylpropane radical cations

Mead, Phillip T.; Donchi, Kevin F.; Traeger, John C.; Christie, John; Derrick, Peter J.

doi:10.1021/ja00530a011

Cited by 24 publications

(8 citation statements)

References 7 publications

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“…It was concluded that hydrogen transfer in methane elimination from ionised acetone does not involve tunnelling, but rather that the isotope effect arises from differences between zero point energies for the transition states for H-and D-transfer. The strong secondary isotope effects observed in a number of other systems 8,12,25 are consistent with this interpretation and demonstrate that isotope effects on zero point energies can strongly affect the RAs of competing reactions of metastable ions, even in circumstances in which tunnelling cannot occur.…”

Section: Methodssupporting

confidence: 65%

“…Methyl radical and methane loss from ionised 2-methylpropane were characterised in 1975 by field ionisation kinetics. 63 Methyl radical loss dominated at short times, but methane elimination was favoured at times longer than about 3 × 10 -11 s. The dissociation patterns of deuterium-labelled 2methylpropane radical-cations obtained in 1980 25 provide another example of secondary isotope effects on an alkane elimination. For example, (CD 3 ) 2 CHCH 3 +• loses CH 3 D almost 8.5 times more often than it loses CHD 3 , so demonstrating a large secondary isotope effect.…”

Section: Ionised 2-methylpropanementioning

confidence: 94%

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EMS Account: Alkane eliminations from ions in the gas phase

McAdoo

Bowen

1999

Eur. J. Mass Spectrom.

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A review of reactions involving the elimination of an alkane from a variety of even and odd electron ions in the gas phase is presented. Particular attention is focused on the mechanisms of these reactions and the role of ion-neutral complexes. Alkane eliminations from open shell species derived by ionisation of ketones, ethers, alcohols, amines, alkanes and alkyl-substituted cycloalkanes are considered, together with ethane loss from the distonic ion CH 2 =O + CH 2 CH 2 •. These reactions are, without obvious exception, complex-mediated. Elimination of alkanes from an assortment of closed shell ions, including protonated acetaldehyde, dialkylmethylene immonium ions, onium ions, quaternary ammonium cations, alkoxide anions, enolate anions and deprotonated amines are also discussed. These reactions tend to be complex-mediated when heterolytic bond cleavages are possible. When such cleavages are not energetically feasible, alkane eliminations can take place by asynchronous, concerted mechanisms. Several factors affect the relative rates of alkane elimination compared to those of competing alkyl radical loss in the dissociations of these radical-cations; these factors include the internal energy of the ion, the size of the ionic and neutral partners, the initial orientation of these components and the binding energy of the complex. In addition, primary and secondary isotope effects influence both alkyl radical and alkane elimination. When alkanes are eliminated from radical-cations, reaction between the partners is often quickly overtaken in importance by direct separation of the components if the internal energy is raised either by increasing the energy of the ionisation process or by prior isomerisation over an energy barrier. This trend demonstrates that the attractions between the partners are easily overcome by quite small amounts of excess energy in the system. Typical binding energies between the ionic and non-polar neutral partners lie in the range 0-30 kJ mol-1 at distances at which covalent forces cease to be significant. Illustrative examples are given to show how studies of reactions involving ion-neutral complexes offer a means of obtaining information on the dynamics of short range interactions between ions and neutrals, including the motions of the partners relative to each other.

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Section: Methodssupporting

confidence: 65%

Section: Ionised 2-methylpropanementioning

confidence: 94%

EMS Account: Alkane eliminations from ions in the gas phase

McAdoo

Bowen

1999

Eur. J. Mass Spectrom.

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“…A large secondary effect of ca. 20 (CH3D over CD4 in the d6 ion) and a small primary effect of 2.5 were taken as evidence that the reaction does not proceed via a concerted four-center mechanism for methane elimination.44 These isotope effects were interpreted in terms of a nonclassical transition state involving a three-center bond analogous to the structure (40) Large intramolecular kinetic isotope effects (both primary and secondary) have been reported for metastable ion decompositions (ref 8,[41][42][43][44]. The internal energy of metastable ions is generally distributed fairly narrowly just above the reaction threshold.…”

Section: Mass Spectrometric Fragmentations40•45mentioning

confidence: 99%

A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion

et al. 1987

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“…However, F can be compared to isotope effects found in elementary ion/molecule reactions. Such a-secondary kinetic isotope effects can be quite large [40,41]. The large effects found in ion/molecule reactions are usually due to a narrow (non-Boltzmann) energy distribution centered close to the threshold energy [42].…”

Section: C3h3' + Czhz/czdzmentioning

confidence: 99%

Kinetic modeling of the reactions of C₃H₃⁺ with acetylene, deuteroacetylene, and diacetylene

Wiseman¹,

Zerner

Eyler

1990

Int J of Chemical Kinetics

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The reactions of e-C3H3' (propargylium cation) with acetylene and diacetylene have been modeled kinetically. Data were obtained from Fourier Transform Ion Cyclotron Resonance (FTICR) experiments on these systems, which are themselves models for soot particle initiation. Acetylene forms an encounter complex with !-C3H3+, but, in the absence of a third body collision, the complex decomposes to acetylene and c-C3H3+ (cyclopropenylium cation) at about 1/3 the rate it decomposes to acetylene and e-C3H3+, in spite of the fact that c -C~H~' is ca. 115 kJ/mol more stable than t-C3H3+. The encounter complex is long enough lived, and energetic enough, to scramble deuterium in reactions between e-C3H3' and CzD2. These reactions have been successfully modeled, yielding a nearly statistical distribution of deuterium, and a rather large kinetic isotope effect. The more complex reactions of e-CsH3' with diacetylene have also been modeled.

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Secondary hydrogen isotope effect in the unimolecular decomposition of 2-methylpropane radical cations

Cited by 24 publications

References 7 publications

EMS Account: Alkane eliminations from ions in the gas phase

EMS Account: Alkane eliminations from ions in the gas phase

A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion

Kinetic modeling of the reactions of C₃H₃⁺ with acetylene, deuteroacetylene, and diacetylene

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Secondary hydrogen isotope effect in the unimolecular decomposition of 2-methylpropane radical cations

Cited by 24 publications

References 7 publications

EMS Account: Alkane eliminations from ions in the gas phase

EMS Account: Alkane eliminations from ions in the gas phase

A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion

Kinetic modeling of the reactions of C3H3+ with acetylene, deuteroacetylene, and diacetylene

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Product

Resources

About

Kinetic modeling of the reactions of C₃H₃⁺ with acetylene, deuteroacetylene, and diacetylene