MNDO-rechnungen zum mechanismus der H2O-abspaltung aus protoniertem cyclohexanon in der gasphase

Heinrich, Nikolaus; Wolfschütz, Roland; Frenking, Gernot; Schwarz, Helmut

doi:10.1016/0020-7381(82)80040-5

Cited by 8 publications

(3 citation statements)

References 36 publications

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“…Its presence was observed only at high collision energy, strongly depending on both the kinetic energy of the preselected species and the collision gas pressure. It is interesting to emphasize that the formation of the ion at m/z 59 was also observed in simple CI spectra obtained using methane as reactant gas:12 in this case, the attainment of the critical energy for the protonated acetone fragment is due to the enthalpy of the protonation reaction (and not to collision phenomena).…”

Section: Resultsmentioning

confidence: 70%

On the detailed mechanisms of collision‐induced dissociation experiments performed by electrospray ion trap

Catinella

Pelizzi

Barboso

et al. 2002

Rapid Comm Mass Spectrometry

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The product ion spectra obtained by electrospray ionization (ESI) ion trap instruments exhibit a higher number of fragment ions than those achieved by other ion-trap-based systems, indicating the presence of more effective energy deposition mechanisms. This behavior can be attributed to several different reasons, among which different initial internal energy of the precursor ions, pre-activation due to collisions taking place outside the trap, different target gas mixtures inside the trap, and different ion trap geometry were considered. Data obtained from experiments using a triple quadrupole instrument, CI-ion trap, and ESI-ion trap have been compared. The results so achieved seem to indicate that the presence inside the trap of neutral molecules of the solvent employed for the ESI process have a relevant role, promoting high energy deposition in the colliding ions.

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Section: Resultsmentioning

confidence: 70%

On the detailed mechanisms of collision‐induced dissociation experiments performed by electrospray ion trap

Catinella

Pelizzi

Barboso

et al. 2002

Rapid Comm Mass Spectrometry

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show abstract

“…The first hydride shift shown in Scheme ( a ) is likely to be the most endothermic step in the reaction sequence (the second hydride shift is exothermic). The enthalpy changes of analogous 1,2-hydride shifts in protonated carbonyl compounds have been estimated to be 30−36 kcal/mol. ,− Hence, the energy released upon adduct formation (≥40 kcal/mol) should be enough to overcome this energy barrier, as indicated in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…The enthalpy changes of analogous 1,2-hydride shifts in protonated carbonyl compounds have been estimated to be 30-36 kcal/ mol. 28,[30][31][32][33] Hence, the energy released upon adduct formation…”

Section: Resultsmentioning

confidence: 99%

Disubstituted Boron Cations Cleave Carbonyl Bonds

1997

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The disubstituted boron cations CH3OBOCH3 + and CH3BCH3 + readily cleave CO and C−C bonds in gaseous long-chain aldehydes and ketones in a dual-cell Fourier transform ion cyclotron resonance mass spectrometer. Abstraction of OH by the borocations yields a hydrocarbon product ion that contains the entire carbon skeleton of the aldehyde or ketone. A competing abstraction of part of the carbonyl compound as a small aldehyde results in a borocation product that is indicative of the location of the carbonyl group in the neutral substrate. The mechanisms of these two reactions likely involve common intermediates formed via 1,2-hydride shifts in an initially formed B−OC adduct. Both reactions are highly exothermic. The OH abstraction reaction is the thermodynamically favored pathway while aldehyde abstraction is kinetically favored by the smaller carbonyl compounds. The overall enthalpy change associated with the latter reaction is likely to be relatively insensitive to the size of the carbonyl compound. In contrast, the OH abstraction reaction becomes more exothermic as the size of the substrate increases. This results in a predominant hydrocarbon ion product for the larger aldehydes and ketones.

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Mindo/3 and mndo calculations of closed‐ and open‐shell cations containing C, H, N, and O

Halim¹,

Heinrich²,

Koch³

et al. 1986

J Comput Chem

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Heats of formation of 119 closed- and open-shell carbocations calculated by the semiempirical quantum chemical methods MINDO/3 and MNDO are reported and compared with experimental data. With proper consideration of failures in specific areas, both methods can be used for the thermodynamics of carbocations containing C, H, N, and O. MINDO/3 predicts unrealistic values for nitrogen containing cations with nitrogen multiple bonds and is not suited for closed-shell cations containing oxygen. Saturated acyclic hydrocarbon radical cations often are computed with abnormally long CC bonds by MNDO. Otherwise, the standard deviation of the two methods is not very different, being in the range of ±13 kcal/mol. MINDO/3 tends to overestimate the cation stabilities, whereas MNDO calculates cations usually too high in energy. Some of the errors which were found in the calculations of the ions are related to the computed values for the parent neutral structures, but others are not.

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MNDO-rechnungen zum mechanismus der H2O-abspaltung aus protoniertem cyclohexanon in der gasphase

Cited by 8 publications

References 36 publications

On the detailed mechanisms of collision‐induced dissociation experiments performed by electrospray ion trap

On the detailed mechanisms of collision‐induced dissociation experiments performed by electrospray ion trap

Disubstituted Boron Cations Cleave Carbonyl Bonds

Mindo/3 and mndo calculations of closed‐ and open‐shell cations containing C, H, N, and O

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