Abstract
Infrared multiple photon (IRMP) photochemical activation of gas-phase ions trapped in an ion cyclotron resonance (ICR) spectrometer has been used to study the mechanism of a gas-phase negative ion unimolecular decomposition. Upon irradiation with a CO2 laser (both high-power pulsed and low-power continuous wave (CW)), tert-butoxide anion, trapped in a pulsed ICR spectrometer, decomposes to yield acetone enolate anion and methane. The mechanism of this formal 1,2-elimination reaction was probed by measuring competitive hydrogen isotope effects (both primary and secondary) in the IR laser photolysis of 2-methyl-2-propoxide-1,1,1-d3 (1) and 2-methyl-2-propoxide-1,1,1,3,3,3-d6 (2) anions. Unusually large secondary isotope effects (pulsed laser, 1.9 for 1 and 1.7 for 2; cw laser, 8 for 1) and small primary isotope effects (pulsed laser, 1.6 for 1 and 2; cw laser, 2.0 for 1) were observed. These isotope effects, particularly the large difference in energy dependence of the primary and secondary effects, are consistent only with a stepwise mechanism involving initial bond cleavage to an intermediate ion-molecule complex followed by a hydrogen transfer within the intermediate complex. The observed secondary isotope effects have been modelled by using statistical reaction rate (RRKM) theory. The implications of this study for several previously reported unimolecular ion decompositions are also discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 961-970 |
| Number of pages | 10 |
| Journal | Journal of the American Chemical Society |
| Volume | 109 |
| Issue number | 4 |
| Publication status | Published - 1987 |
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A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion. / Tumas, William; Foster, Robert F.; Pellerite, Mark J.; Brauman, John I.
In: Journal of the American Chemical Society, Vol. 109, No. 4, 1987, p. 961-970.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion
AU - Tumas, William
AU - Foster, Robert F.
AU - Pellerite, Mark J.
AU - Brauman, John I.
PY - 1987
Y1 - 1987
N2 - Infrared multiple photon (IRMP) photochemical activation of gas-phase ions trapped in an ion cyclotron resonance (ICR) spectrometer has been used to study the mechanism of a gas-phase negative ion unimolecular decomposition. Upon irradiation with a CO2 laser (both high-power pulsed and low-power continuous wave (CW)), tert-butoxide anion, trapped in a pulsed ICR spectrometer, decomposes to yield acetone enolate anion and methane. The mechanism of this formal 1,2-elimination reaction was probed by measuring competitive hydrogen isotope effects (both primary and secondary) in the IR laser photolysis of 2-methyl-2-propoxide-1,1,1-d3 (1) and 2-methyl-2-propoxide-1,1,1,3,3,3-d6 (2) anions. Unusually large secondary isotope effects (pulsed laser, 1.9 for 1 and 1.7 for 2; cw laser, 8 for 1) and small primary isotope effects (pulsed laser, 1.6 for 1 and 2; cw laser, 2.0 for 1) were observed. These isotope effects, particularly the large difference in energy dependence of the primary and secondary effects, are consistent only with a stepwise mechanism involving initial bond cleavage to an intermediate ion-molecule complex followed by a hydrogen transfer within the intermediate complex. The observed secondary isotope effects have been modelled by using statistical reaction rate (RRKM) theory. The implications of this study for several previously reported unimolecular ion decompositions are also discussed.
AB - Infrared multiple photon (IRMP) photochemical activation of gas-phase ions trapped in an ion cyclotron resonance (ICR) spectrometer has been used to study the mechanism of a gas-phase negative ion unimolecular decomposition. Upon irradiation with a CO2 laser (both high-power pulsed and low-power continuous wave (CW)), tert-butoxide anion, trapped in a pulsed ICR spectrometer, decomposes to yield acetone enolate anion and methane. The mechanism of this formal 1,2-elimination reaction was probed by measuring competitive hydrogen isotope effects (both primary and secondary) in the IR laser photolysis of 2-methyl-2-propoxide-1,1,1-d3 (1) and 2-methyl-2-propoxide-1,1,1,3,3,3-d6 (2) anions. Unusually large secondary isotope effects (pulsed laser, 1.9 for 1 and 1.7 for 2; cw laser, 8 for 1) and small primary isotope effects (pulsed laser, 1.6 for 1 and 2; cw laser, 2.0 for 1) were observed. These isotope effects, particularly the large difference in energy dependence of the primary and secondary effects, are consistent only with a stepwise mechanism involving initial bond cleavage to an intermediate ion-molecule complex followed by a hydrogen transfer within the intermediate complex. The observed secondary isotope effects have been modelled by using statistical reaction rate (RRKM) theory. The implications of this study for several previously reported unimolecular ion decompositions are also discussed.
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M3 - Article
VL - 109
SP - 961
EP - 970
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 4
ER -