Identity-reaction proton transfers from oxygen acids yielding localized vs. delocalized conjugate bases. An ab initio study

Identity-reaction proton transfers from a series of oxygen acids to the corresponding conjugate bases have been studied by ab initio methods at the MP2/6-31+G*//MP2/6-31+G* level. The acids are H3O+, CH3OH2+, CH2 = OH+, HC(O)OH2+, CH2 = CHOH2+, H2O, CH3OH, HOOH, HOCH2OH, FOH, FCH2OH, HC(O)OH, and CH2 = CHOH. Gas-phase acidities were calculated at the G2(MP2) level in order to have benchmark values for all acidities regardless of whether experimental values were available. Barriers to proton transfer relative to the separated reactants, ΔHTS, show a straight-line relation to acidity for all but two of the neutral acids and for all but one of the cationic acids. Two neutral acids, HOOH and FOH, show negative deviations that can be attributed to polarizability of the atoms attached to the proton donor oxygens. The cationic acid HC(O)OH2+ shows a large positive deviation, which probably arises from substantial heavy-atom reorganization from reactant to TS. Charges provide evidence of a lag in delocalization in the reaction of CH2 = CHOH2+, though it does not show an elevated ΔHTS.Key words: ab initio, oxygen acids, proton transfer, acidity.

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Identity-reaction proton transfers from nitrogen acids yielding localized vs. delocalized conjugate bases. An ab initio study

Canadian Journal of Chemistry ◽

10.1139/v98-053 ◽

1998 ◽

Vol 76 (6) ◽

pp. 821-827 ◽

Cited By ~ 3

Author(s):

James E. Van Verth ◽

William H Saunders, Jr. ◽

Thomas W Kermis

Keyword(s):

Proton Transfer ◽

Ab Initio ◽

Negative Deviation ◽

Proton Transfers ◽

Straight Line ◽

Transition Structures ◽

Pi Systems ◽

Experimental Values ◽

Small Negative Deviation ◽

Conjugate Bases

Identity-reaction proton transfers from a series of nitrogen acids to the corresponding conjugate bases have been studied by ab initio methods at the MP2/6-31+G*//MP2/6-31+G* level. The acids are NH4+, H2NNH3+, CH3NH3 +, CH2NH2, OCNH 2+, OCHNH3+, H2NCHNH2+ , HNCHNH 3+, NH3, CH3NH2, CH2NH, OCNH, OCHNH2,and HNCHNH2. Gas-phase acidities were calculated at the G2(MP2) level where experimental values are not available in order to have benchmark values for all acidities. Barriers to proton transfer relative to the separated reactants, ΔHTS, show a straight-line relation to acidity for all of the neutral acids and for all but four of the cationic acids. Three show ΔHTS values well above the line: HNCHNH3+, OCNH2+, and OCHNH3 +, in increasing order of positive deviation. One shows a small negative deviation: H2NNH3+ . The first three acids have localized pi systems but can yield delocalized transition structures and conjugate bases. The barriers result from a lag in delocalization relative to proton transfer in the transition structures. All of the other acids give transition structures that can only be localized, or if they can be delocalized they prefer to adopt conformations in which the unshared pair on nitrogen delocalizes rather than the electrons of the N---H bond. The negative deviation for H2NNH3 + is attributed to polarizability of the NH2 group.Key words: ab initio, nitrogen acids, proton transfer, acidity.

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Is There a Transition-State Imbalance for Proton Transfers in the Gas Phase? Ab Initio Study of the Carbon-to-Carbon Proton Transfer from Acetaldehyde to Its Enolate Ion

Journal of the American Chemical Society ◽

10.1021/ja00091a052 ◽

1994 ◽

Vol 116 (12) ◽

pp. 5405-5413 ◽

Cited By ~ 26

Author(s):

Claude F. Bernasconi ◽

Philip J. Wenzel

Keyword(s):

Proton Transfer ◽

Transition State ◽

Ab Initio ◽

Gas Phase ◽

Ab Initio Study ◽

Proton Transfers

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Ab Initio Study of the Carbon-to-Carbon Identity Proton Transfer from Ketene to Its Anion in the Gas Phase

Journal of the American Chemical Society ◽

10.1021/ja003858x ◽

2001 ◽

Vol 123 (10) ◽

pp. 2430-2431 ◽

Cited By ~ 4

Author(s):

Claude F. Bernasconi ◽

Philip J. Wenzel

Keyword(s):

Proton Transfer ◽

Ab Initio ◽

Gas Phase ◽

Ab Initio Study

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Proton transfer between carbon acids and methoxide: Studies in methanol, the gas phase and by ab initio MO calculations

Berichte der Bunsengesellschaft für physikalische Chemie ◽

10.1002/bbpc.19981020341 ◽

1998 ◽

Vol 102 (3) ◽

pp. 567-572 ◽

Cited By ~ 3

Author(s):

Heinz F. Koch ◽

Masaaki Mishima ◽

Han Zuilhof

Keyword(s):

Proton Transfer ◽

Ab Initio ◽

Gas Phase ◽

Mo Calculations ◽

Ab Initio Mo Calculations ◽

Carbon Acids ◽

Ab Initio Mo

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Ab initio Predictions of the Gas-Phase Acidities of Diazirine and Diazomethane

Australian Journal of Chemistry ◽

10.1071/ch9950401 ◽

1995 ◽

Vol 48 (2) ◽

pp. 401 ◽

Cited By ~ 2

Author(s):

AJ Russell ◽

AP Scott ◽

L Radom

Keyword(s):

Ab Initio ◽

Gas Phase ◽

Molecular Orbital ◽

Calculated Result ◽

Molecular Orbital Calculations ◽

Experimental Values

Absolute gas-phase acidities of diazirine, diazomethane, dimethylamine, ethylamine and methylamine have been obtained with ab initio molecular orbital calculations at the G2 and G2(MP2) levels of theory. Values at the G2 and G2(MP2) levels are all within 1 kJ mol-1 of one another. The calculated gas-phase acidities for diazomethane, dimethylamine, ethylamine and methylamine (and other reference molecules considered) are all within 3 kJ mol-1 of experiment. For diazirine the calculated result, although consistent with experiment, would suggest an acidity towards the lower end of the range of possible experimental values.

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Gas-phase and solution-phase proton transfer to H2O analyzed by high-level ab initio quantum chemistry including complete basis set and Gaussian theory schemes

Chemical Physics Letters ◽

10.1016/s0009-2614(99)00134-7 ◽

1999 ◽

Vol 302 (5-6) ◽

pp. 471-479 ◽

Cited By ~ 17

Author(s):

Gerrit Schüürmann

Keyword(s):

Quantum Chemistry ◽

Proton Transfer ◽

Ab Initio ◽

Gas Phase ◽

Solution Phase ◽

Basis Set ◽

Complete Basis ◽

Complete Basis Set ◽

Gaussian Theory ◽

High Level

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The carbanion mechanism of olefin-forming elimination. VIII. Theoretical analysis of substituent and isotope effects in proton transfers from 2,2-Diaryl-1,1,1-trichloroethanes

Australian Journal of Chemistry ◽

10.1071/ch9760787 ◽

1976 ◽

Vol 29 (4) ◽

pp. 787 ◽

Cited By ~ 7

Author(s):

DJ McLennan ◽

RJ Wong

Keyword(s):

Proton Transfer ◽

Rate Constants ◽

Isotope Effects ◽

Reaction Series ◽

Free Energy Of Activation ◽

Proton Transfers ◽

Parabolic Relationship ◽

Equilibrium Data ◽

Pass Through ◽

Experimental Values

Rate constants for the dehydrochlorination of the title compounds by anionic bases in alcoholic solvents are those for simple proton transfer. Rate and estimated equilibrium data for these reactions can be approximately analysed in terms of the Marcus theory of proton transfer. In one reaction series comprising the reactions of para-substituted Ar2CHCC13 compounds with NaOMe in MeOH, the work term (wr) and the intrinsic free energy of activation (ΔG?) are comparable and large. The change in kH/kD with variation in substituent can be quantitatively rationalized, and the fact that kH/kD does not pass through a maximum even though ΔpK = 0 within the series can be understood. Although the required rate-equilibrium parabolic relationship for a second series involving the reactions of (p-ClC6H4)2CHCCl3 with a series of bases is obtained, anomalous Marcus parameters are derived, and reasons for the anomalies are given. A revised set of approximate pKa values for Ar2CHCCl3 compounds is presented, and more precise experimental values of rate constants for the reactions of (p-NO2C6H4)2CHCC13 and (p-NO2C6H4)2CDCCl3 with NaOMe in MeOH are provided.

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