Isotope effects as a mechanistic probe of unimolecular ion decompositions. tert-Butoxide anion

Tumas, William; Foster, Robert F.; Pellerite, Mark J.; Brauman, John I.

doi:10.1021/ja00363a055

Cited by 48 publications

(22 citation statements)

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“…Thus as reported previously (28,29,31), t-butoxide (entry 7) eliminates CH4, while the t-pentoxide ion (entry 13) shows elimination of CH4 and, in minor yield, CzH6.…”

Section: Acknowledgementssupporting

confidence: 82%

“…The scheme has been constructed on the basis of the step-wise mechanism proposed by Bowie and co-workers (27,28) and Brauman and co-workers (29)(30)(31). Although the simple bond fission products (H-and CH3-) were not observed they are included in this and following schemes because they provide information relevant to the energies of the intermediate ion-dipole complexes.…”

Section: Fig 1 Breakdown Graph For I-propoxide (Mlz 59)mentioning

confidence: 99%

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Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

Mercer¹,

Harrison²

1988

Can. J. Chem.

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. Can. J. Chem. 66, 2947Chem. 66, (1988.The collisionally activated dissociation reactions of the C2 to C5 alkoxide ions have been studied for collisons occurring at 8 keV kinetic energy and also over the range 5 to 100 eV kinetic energy. The alkoxide ions fragment by 1,2-elimination of H2 andlor an alkane. Thus, primary alkoxide ions fragment by elimination of H, only, secondary alkoxide ions show elimination of Hz and alkane molecules, while tertiary alkoxide ions show elimination of alkanes only. In alkane elimination, loss of CH4 is much more facilie than loss of larger alkanes. For secondary alkoxide ions, where more than one elimination reaction occurs, the energy dependence of fragmentation has been explored over the collision energy range 5 to 100 eV. The results are interpreted in terms of a step-wise mechanism involving formation of an anion-carbonyl compound ion-dipole complex, followed by proton abstraction by the H-or alkyl anion leading to the final products. The relative importance of the reaction channels is determined by the relative stabilities of these ion-dipole complexes. ROGER S. MERCER et ALEX G. HARRISON. Can. J. Chem. 66,2947 (1988.On a CtudiCe les reactions de dissociation des ions alcoolates C2 a CS activkes par des collisions se produisant i une Cnergie cinktique de 8 keV ainsi qu'i des energies cinetiques allant de 5 a 100 eV. Les ions alcoolates se fragmentent par une elimination-l,2 de Hz eVou d'alcane. Ainsi, les ions alcoolates primaires se fragmentent uniquement par une elimination de Hz; par ailleurs, les ions alcoolates secondaires presentent de l'elimination de H2 ainsi que celle de molecules d'alcanes alors que les ions alcoolates tertiaires ne presentent que de l'elimination d'alcanes. Lors de l'elimination d'alcanes, la perte de CH4 est beaucoup plus facile que celle des alcanes plus volumineux. Dans le cas des alcoolates secondaires oh il se produit plus d'une elimination, on a CvaluC la relation qui existe entre I'energie de collision (de 5 100 eV) et le type de fragmentation. On interprete les resultats en fonction d'un mecanisme par Ctape impliquant la formation d'un complexe ion-dip6le d'un compose anioncarbonyle, suivie par l'enlevernent d'un proton par un H-ou par un anion alkyle, conduisant aux produits. On a determine l'importance relative des diverses voies rtactionnelles en se basant sur les stabilites relatives de ces complexes ion-dip6les.[Traduit par la revue] Introduction Studies of the fragmentation of gaseous ions have long been invaluable sources of information concerning the structures and chemistry of such species (1, 2). This information is even more useful if the internal energy of the fragmenting ions is known and can be varied in a controlled fashion; such energy-resolved studies permit the establishment of break-down graphs expressing the variation of fragment ion yields with internal energy. Energy-resolved data for odd-electron molecular cations can be obtained with high precision by photoelectron/photoion coincidence (PEPICO) experiments (3-5)...

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“…Thus as reported previously (28,29,31), t-butoxide (entry 7) eliminates CH4, while the t-pentoxide ion (entry 13) shows elimination of CH4 and, in minor yield, CzH6.…”

Section: Acknowledgementssupporting

confidence: 82%

Section: Fig 1 Breakdown Graph For I-propoxide (Mlz 59)mentioning

confidence: 99%

Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

Mercer¹,

Harrison²

1988

Can. J. Chem.

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“…Firstly, loss of CH 2 O is the basic cleavage of a benzyloxy anion: 5 this will produce product ion p-OHC-C 6 H 4 in this case. Second, a major fragmentation route of an alkoxide anion proceeds via an ion complex 6 (Fig. 2), establish that a cross-ring hydride S N i (S N 2 type) reaction is occurring in this system.…”

Section: Resultsmentioning

confidence: 81%

Mobility of anions within anion-neutral complexes. Cross ring hydride ion migration upon collisional activation of thepara-formylbenzyloxy anion

Dua

Bowie

1997

Rapid Commun. Mass Spectrom.

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“…Estimation of the densities of vibrational states demonstrated that for the dimer the quasi-continuum is reached by absorption of only one photon whereas absorption of four photons is necessary to access the quasi-continuum for the monomer. Infrared multiphoton dissociation (IRMPD) of small polyatomic ions with low-power CW lasers has been studied by a number of groups (Bomse & Beauchamp, 1981a,b;Bomse, Berman, & Beauchamp, 1981;Jasinski et al, 1982, Tumas et al, 1983Baykut et al, 1985;Shin & Beauchamp, 1990;Dunbar, 1991;Uechi & Dunbar, 1992;Dunbar & Zaniewski, 1992;. Early studies have been reviewed by Thorne & Beauchamp (1984).…”

Section: Multiphoton Dissociationmentioning

confidence: 99%

Activation of large lons in FT‐ICR mass spectrometry

Laskin

Futrell

2004

Mass Spectrometry Reviews

175

146

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The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition-the kinetic shift (KS). The longer trapping time of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules. After discussing general principles of reaction dynamics related to collisional activation of ions, we describe conventional ways to achieve single-and multiple-collision activation in FT-ICR MS. Sustained off-resonance irradiation (SORI)-the simplest and most robust means of introducing the multiple collision activation process-is discussed in greatest detail. Details of implementation of this technique, required control of experimental parameters, limitations, and examples of very successful application of SORI-CID are described. The advantages of high mass resolving power and the ability to carry out several stages of mass selection and activation intrinsic to FT-ICR MS are demonstrated in several examples. Photodissociation of ions from small molecules can be effected using IR or UV/vis lasers and generally requires tuning lasers to specific wavelengths and/ or utilizing high flux, multiphoton excitation to match energy levels in the ion. Photodissociation of complex ions is much easier to accomplish from the basic physics perspective. The quasi-continuum of vibrational states at room temperature makes it very easy to pump relatively large amounts of energy into complex ions and infrared multiphoton dissociation (IRMPD) is a powerful technique for characterizing large ions, particularly biologically relevant molecules. Since both SORI-CID and IRMPD are slow activation methods they have many common characteristics. They are also distinctly different because SORI-CID is intrinsically selective (only ions that have a cyclotron frequency close to the frequency of the excitation field are excited), whereas IRMPD is not (all ions that reside on the optical path of the laser are excited). There are advantages and disadvantages to each technique and in many applications they complement each other. In contrast wi...

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Isotope effects as a mechanistic probe of unimolecular ion decompositions. tert-Butoxide anion

Cited by 48 publications

References 0 publications

Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

Mobility of anions within anion-neutral complexes. Cross ring hydride ion migration upon collisional activation of thepara-formylbenzyloxy anion

Activation of large lons in FT‐ICR mass spectrometry

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