Structure of isomeric anions in the gas phase: arylallyl and arylcyclopropyl anions

Andrist, A. Harry; DePuy, Charles H.; Squires, Robert R.

doi:10.1021/ja00316a003

Cited by 17 publications

(9 citation statements)

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“…However, with 6 and more H 2 O molecules, the Nprotonated tautomer (i.e., the more stable tautomer in protic liquid) was more stable and abundant. This interconversion via the proton shuttling efforts of polar molecules (e.g., H 2 O, CH 3 OH) has also been suggested for many other small ionic isomer systems (e.g., distonic and conventional radical cations) [7][8][9][10][11][12]36], although none were separated prior to analysis in the gas-phase as DMS has provided here.…”

Section: Resultssupporting

confidence: 60%

“…For clusters containing a single CH 3 OH molecule,~10,000 structures were sampled. This increased tõ 30,000 structures for the (4-ABA•H + )(CH 3 OH) 8 cluster. Each BH iteration was subject to prescreening with volume and geometry constraints, which ensured that the clusters did not dissociate and that atoms did not occupy the same volume.…”

Section: Methodsmentioning

confidence: 94%

“…In rare cases, orthogonal separation of tautomers prior to MS analysis could be afforded by gas chromatography [4], but the vast majority of cases involve MS analysis of convolved mixtures of tautomers. As such, the probing of tautomeric systems with MS has consisted of observing the relative ratios of tautomers and their fragment ions by adjusting ionization conditions [5], adjusting the energy of a tandem mass spectrometry (MS/MS) event [6], using diagnostic ion/molecule reactions [7][8][9][10][11][12], probing with ion spectroscopy [13,14], or through the assistance of computational modeling to confirm the presence and behavior of a given tautomer [15].…”

Section: Introductionmentioning

confidence: 99%

“…Depending upon that environment, the mechanism of gas-phase HDX [35,36] should also be considered. In addition, while HDX generally probes static noninterconvertible structures [37][38][39], it can also serve to catalyze interconversion (tautomerization) [7][8][9][10][11][12], thereby complicating the characterization of subtle structural features by MS. However, in the gas-phase HDX studies cited here, the only mechanism for tautomer identification was by observation of changes in ion reactivity within convolved populations; no mechanism for separation of these tautomers before or after identification was available.…”

Section: Introductionmentioning

confidence: 99%

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Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

Campbell

Yang

Melo

et al. 2016

J. Am. Soc. Mass Spectrom.

125

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Abstract. In this study, we report on the use of differential mobility spectrometry (DMS) as a tool for studying tautomeric species, allowing a more in-depth interrogation of these elusive isomers using ion/molecule reactions and tandem mass spectrometry. As an example, we revisit a case study in which gas-phase hydrogendeuterium exchange (HDX)-a probe of ion structure in mass spectrometry-actually altered analyte ion structure by tautomerization. For the N-and O-protonated tautomers of 4-aminobenzoic acid, when separated using DMS and subjected to subsequent HDX with trace levels of D 2 O, the anticipated difference between the exchange rates of the two tautomers is observed. However, when using higher levels of D 2 O or a more basic reagent, equivalent and almost complete exchange of all labile protons is observed. This second observation is a result of the interconversion of the N-protonated tautomer to the Oprotonated form during HDX. We can monitor this transformation experimentally, with support from detailed molecular dynamics and electronic structure calculations. In fact, calculations suggest the onset of bulk solution phase properties for 4-aminobenzoic acid upon solvation with eight CH 3 OH molecules. These findings also underscore the need for choosing HDX reagents and conditions judiciously when separating interconvertible isomers using DMS.

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Section: Resultssupporting

confidence: 60%

Section: Methodsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

Campbell

Yang

Melo

et al. 2016

J. Am. Soc. Mass Spectrom.

125

View full text Add to dashboard Cite

show abstract

“…mol "! more acidic than suggested by two previous independent studies [22,32] where PA bracketing of deprotonated pheny1cyclopropane, generated by deprotonation of the parent neutral molecule by OH-under FA conditions, indicated that the acidity of phenylcyclopropane is very close to the acidity of water (AGo. cid = 1607 kJ mol-I).…”

Section: Materij:llsmentioning

confidence: 71%

On the stabilization of carbanions by adjacent phenyl, cyano, methoxy-carbonyl, and nitro groups in the gas phase

Peerboom

Koning

Nibbering

1994

J. Am. Soc. Mass Spectrom.

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Institute of Mass Spectrometry, University of Amsterdam, Amsterdam, The Netherlands By using the method of Fourier transform ion cyclotron resonance mass spectrometry, substituent stabilization energies of homologous series of cycloalkyl carbanions, Ξ-c-CnH2n-2 (n = 3, 4, 5, 6, 7) with π-accepting substituents (Ξ = Ph, CN, COOMe, NO2) have been determined experimentally in the gas phase as the difference between the proton affinity of the substituted and corresponding unsubstituted (Ξ = H) cycloalkyl carbanions.The stabilization energy data have been analyzed in terms of Taft's parametrization of polarizability, field/inductive, and resonance effects. The linear regression analyses show excellent correlations within the ΞCH2 (-) Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7), and Ξ-c-C3H4 (-) carbanion series, from which it appears that the contributions of polarizability effects are independent of the above type of carbanions and only depend on the nature of the substituent.Further, it follows that inductive stabilization is more effective in the substituted methyl, ΞCH2 (-), than in the substituted cycloalkyl, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7) carbanions. This result suggests that inductive stabilization is counteracted by the electron releasing effect of alkyl groups.Resonance stabilization is significantly more effective in the substituted cycloalkyl, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7), than in the substituted methyl, ΞCH2 (-), carbanions, which suggests that m contrast to inductive stabilization, resonance stabilization is assisted by the electron releasing effect of alkyl groups.Finally, it appears that substitutent stabilization in the geometrically restricted substituted cyclopropyl carbanions, Ξ-c-C3H4 (-), is dramatically less effective than in the corresponding geometrically unrestricted larger substituted cycloalkyl carbanions, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7). The linear regression analyses of the substituted cycloalkyl carbanions indicate that reduction of the stabilization energy is caused not exclusively by a geometrically hindered resonance stabilization, but also to a smaller extent by a less efficient inductive stabilization in the substituted cyclopropyl carbanions.

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Organoalkali Chemistry

Schlosser

2013

Organometallics in Synthesis

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Structure of isomeric anions in the gas phase: arylallyl and arylcyclopropyl anions

Cited by 17 publications

References 0 publications

Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

Studying Gas-Phase Interconversion of Tautomers Using Differential Mobility Spectrometry

On the stabilization of carbanions by adjacent phenyl, cyano, methoxy-carbonyl, and nitro groups in the gas phase

Organoalkali Chemistry

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