Intrinsic gas-phase acidity and electrophilicity of model heterocations and carbocations relative to pyridine: Adduct formation versus α- or β-(proton transfer) elimination

Measurements of the gas phase proton transfer equilibrium [1]: AH + B− = A− + BH with a pulsed electron high pressure mass spectrometer (PHPMS) lead to [Formula: see text] and [Formula: see text] data. These relative acidities are converted to the absolute acidities [2]: AH = A− + H+bycalibration of the relative [Formula: see text] and [Formula: see text] scale to the known values for [Formula: see text] and [Formula: see text] of a reference compound(HCl). Earlier determinations that included 16 aliphatic AH are extended in the present work and provide data for 47 aliphatic carboxylic acids. These include halogen, OH, CH3O, C2H5O, PhO, and NH2 substituted acetic acids, and halogen substituted, unsaturated, and cyclic RCO2H of higher carbon number. The effects of the various substituents on the gas phase acidity are briefly examined. Keywords: acidities in gas phase, proton transfer equilibria, ion-molecule equilibria, mass spectrometry.

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Intrinsic Acidities of α, β, γ Chlorosubstituted Aliphatic Acids from Gas Phase Equilibrian Mesurements

Canadian Journal of Chemistry ◽

10.1139/v74-137 ◽

1974 ◽

Vol 52 (5) ◽

pp. 861-863 ◽

Cited By ~ 18

Author(s):

R. Yamdagni ◽

P. Kebarle

Keyword(s):

Proton Transfer ◽

Gas Phase ◽

Equilibrium Constants ◽

Transfer Reactions ◽

Pulsed Electron Beam ◽

Aliphatic Acids ◽

Gas Phase Acidity ◽

Proton Transfer Reactions ◽

The Difference ◽

Acidity Scale

Measurements of the proton transfer equilibria: A1− + A2H = A2− with a pulsed electron beam high pressure mass spectrometer were extended to α, β, γ chlorosubstituted aliphatic acids. The equilibrium constants were used to evaluate ΔG0 for the proton transfer reactions. Assuming ΔG ≈ ΔH and using standard acids AH for which the difference between the bond dissociation energy D(A—H) and the electron affinity of A, EA(A) was known one could evaluate the corresponding difference for the newly measured acids and place them on an absolute acidity scale. The gas phase acidity was observed to increase in the order: acetic, propionic, butyric, γ-Cl butyric, β-Cl butyric, β-Cl propionic, α-Cl butyric, α-Cl propionic, α-Cl acetic. The gas phase acidities are compared with those observed in aqueous solution. The effects of the Cl substituent parallel those in solution but are much larger. The attenuation occurring in solution is attributed to weaker hydrogen bonding of the chloro stabilized acid anions to water molecules.

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Substituent and solvent effects on organic acids: an electrostatic theory

Canadian Journal of Chemistry ◽

10.1139/v76-183 ◽

1976 ◽

Vol 54 (8) ◽

pp. 1296-1299 ◽

Cited By ~ 16

Author(s):

Takeki Matsui ◽

Loren G. Hepler

Keyword(s):

Proton Transfer ◽

Organic Acids ◽

Gas Phase ◽

Solvent Effects ◽

Transfer Reactions ◽

Electrostatic Model ◽

Environmental Models ◽

Gas Phase Acidity ◽

Proton Transfer Reactions ◽

Electrostatic Theory

We have used an electrostatic model as basis for derived equations to represent the effects of substituents and solvents on the thermodynamics of proton transfer reactions. Equations derived in this manner are related to those based on earlier 'internal-environmental' models and are also discussed in relation to recent gas phase acidity work.

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Gas Phase Reactions of 1,3,5-Triazine: Proton Transfer, Hydride Transfer, and Anionic σ-Adduct Formation

Journal of the American Society for Mass Spectrometry ◽

10.1007/s13361-011-0133-9 ◽

2011 ◽

Vol 22 (7) ◽

pp. 1260-1272 ◽

Cited By ~ 15

Author(s):

John M. Garver ◽

Zhibo Yang ◽

Shuji Kato ◽

Scott W. Wren ◽

Kristen M. Vogelhuber ◽

...

Keyword(s):

Proton Transfer ◽

Gas Phase ◽

Hydride Transfer ◽

Adduct Formation ◽

Gas Phase Reactions

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Summary of gas phase acidity measurements involving acids AH. Entropy changes in proton transfer reactions involving negative ions. Bond dissociation energies D(A—H) and electron affinities EA(A)

Canadian Journal of Chemistry ◽

10.1139/v78-001 ◽

1978 ◽

Vol 56 (1) ◽

pp. 1-9 ◽

Cited By ~ 156

Author(s):

J. B. Cumming ◽

P. Kebarle

Keyword(s):

Proton Transfer ◽

Gas Phase ◽

Negative Ions ◽

Bond Dissociation Energies ◽

Electron Affinities ◽

Bond Dissociation ◽

Dissociation Energies ◽

Entropy Changes ◽

Gas Phase Acidity ◽

Proton Transfer Reactions

The complete ladder of ΔG10 determinations obtained from measurements of some 110 gas phase proton transfer equilibria A1− + A2H = A1H + A2− involving some 60 acids AH and connecting to the standard acid HCl is given. Evaluation of the entropy changes leads to values for the deprotonation energies ΔHD0 and ΔGD0 (at room temperature) corresponding to the gas phase process AH = A− + H+; ΔHD0 = D(A—H) − EA(A) + 313.6 kcal/mol. Comparison of the present data with literature determinations of the bond dissociation energies and electron affinities shows agreement within 2 kcal/mol. Some experimentally determined entropy changes ΔS10 are compared with the theoretically calculated values.

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