The gas-phase acidities of the alkanes

DePuy, Charles H.; Gronert, Scott; Barlow, Stephan E.; Bierbaum, Veronica M.; Damrauer, Robert

doi:10.1021/ja00188a003

Cited by 156 publications

(138 citation statements)

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“…In Squires and co-workersÏ work on radicals,35,36 the dissociating ions (dimer surrogates) contain a common moiety (the calibrant), and either a reference radical or the unknown. The alkyltrimethylsilaneÈhydroxide ion reaction of DePuy et al 37 represents another similar case. In all these experiments, the calibrant or the references can be chosen for their special properties (lack of steric interactions in the cluster ion, ability to generate clusters readily, well established affinity value, appropriate binding energy for fragmentation on the experimental time scale, etc.)…”

Section: Origins and Characteristics Of The Kinetic Methodsmentioning

confidence: 93%

The kinetic method of making thermochemical determinations

1999

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Section: Origins and Characteristics Of The Kinetic Methodsmentioning

confidence: 93%

The kinetic method of making thermochemical determinations

1999

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“…The latter promptly loses CO 2 from the anionic C terminus, as in Equation (1). This gives the C-terminal À CH 2 À anion that has a higher proton affinity (PA) than À COO À (the gas-phase acidity DG acid of CH 3 CH 3 is 1723 kJ mol À1 , [25] compared to 1427 kJ mol À1 for CH 3 COOH [26] ). The higher proton affinity of the À CH 2 À group weakens the anion-proton binding and disrupts the salt bridge, resulting in monomer separation.…”

Section: -Bradykinin [M+h]mentioning

confidence: 99%

Zwitterionic States in Gas‐Phase Polypeptide Ions Revealed by 157‐nm Ultra‐Violet Photodissociation

Kjeldsen

Silivra

Zubarev

2006

Chemistry A European J

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A new method of detecting the presence of deprotonation and determining its position in gas-phase polypeptide cations is described. The method involves 157-nm ultra-violet photodissociation (UVPD) and is based on monitoring the losses of CO2 (44 Da) from electronically excited deprotonated carboxylic groups relative to competing COOH losses (45 Da) from neutral carboxylic groups. Loss of CO2 is a strong indication of the presence of a zwitterionic [(+)...(-)...(+)] salt bridge in the gas-phase polypeptide cation. This method provides a tool for studying, for example, the nature of binding within polypeptide clusters. Collision-activated dissociation (CAD) of decarboxylated cations localizes the position of deprotonation. Fragment abundances can be used for the semiquantitative assessment of the branching ratio of deprotonation among different acidic sites, however, the mechanism of the fragment formation should be taken into account. Cations of Trp-cage proteins exist preferentially as zwitterions, with the deprotonation position divided between the Asp9 residue and the C terminus in the ratio 3:2. The majority of dications of the same molecule are not zwitterions. Furthermore, 157-nm UVPD produces abundant radical cations M*+ from protonated molecules through the loss of a hydrogen atom. This method of producing M*+ ions is general and can be applied to any gas-phase peptide cation. The abundance of the molecular radical cations M*+ produced is sufficient for further tandem mass spectrometry (MS/MS), which, in the cases studied, yielded side-chain loss of a basic amino acid as the most abundant fragmentation channel together with some backbone cleavages.

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“…[6,7] On the other hand, the acid/ base equilibration between two neutral species and the respective anions allows one to directly monitor just the least basic of several species, for example ortho-fluorobenzenide upon deprotonation of fluorobenzene or 2,3,6-trifluorobenzenide from 1,2,4-trifluorobenzene. To assess the meta and para isomers [8] one has to rely on the silane-cleavage technique [9] or another kinetic method which may not always be free of artifacts. Under such circumstances quantum-chemical calculations may provide a more complete picture and, possibly, be more accurate.…”

Section: Introductionmentioning

confidence: 99%

The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

Hyla‐Kryspin¹,

Büker²,

Nibbering³

et al. 2005

Chemistry A European J

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The deprotonation energies of benzene, fluorobenzene, all di-, tri-, and tetrafluorobenzenes, pentafluorobenzene, chlorobenzene, all di-, tri-, and tetrachlorobenzenes, and pentachlorobenzene have been calculated at various levels of second-order Moller-Plesset and density functional theory. Taking the previously determined experimental data as a benchmark, good agreement was achieved in the chloro series even with moderate computational effort, whereas more extended basis sets have to be used to obtain meaningful numbers in the fluoro series. Apparently, most extensive electron correlation is required to avoid artifacts caused by the proximity of nonbonding lone pairs at the carbanionic center and at the fluorine atoms. When two or more fluorine substituents were introduced in the same aromatic ring, their individual effects (as defined by position-dependent acidity increments) proved to be perfectly additive in the entire series. In contrast, the acidifying effect of chloro substituents was found to level off when the number of such halogens increases. Additivity or non-additivity of element effects cannot be ascertained after having merely compared the acidity of mono- and disubstituted substrates, but only after having moved to higher degrees of substitution.

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The gas-phase acidities of the alkanes

Cited by 156 publications

References 0 publications

The kinetic method of making thermochemical determinations

The kinetic method of making thermochemical determinations

Zwitterionic States in Gas‐Phase Polypeptide Ions Revealed by 157‐nm Ultra‐Violet Photodissociation

The Gas Phase Acidity of Oligofluorobenzenes and Oligochlorobenzenes: About the Additivity or Non‐Additivity of Substituent Effects

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