Ab Initio Comparison of Identity-Reaction Proton Transfers from Carbon Acids Yielding Localized vs. Delocalized Conjugate Bases

1995 ◽  
Vol 60 (11) ◽  
pp. 3452-3458 ◽  
Author(s):  
William H. Saunders ◽  
James E. Van Verth
Keyword(s):  
Ab Initio ◽  
Proton Transfers ◽  
Carbon Acids ◽  
Conjugate Bases

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

1999 ◽  
Vol 77 (5-6) ◽  
pp. 810-816 ◽  
Author(s):  
James E Van Verth ◽  
William H Saunders, Jr.
Keyword(s):  
Proton Transfer ◽  
Ab Initio ◽  
Gas Phase ◽  
Heavy Atom ◽  
Proton Donor ◽  
Proton Transfers ◽  
Straight Line ◽  
Large Positive Deviation ◽  
Experimental Values ◽  
Conjugate Bases

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.

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

1998 ◽  
Vol 76 (6) ◽  
pp. 821-827 ◽  
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.

Kinetics of Proton Transfer Reactions of Carbon Acids. II. Reaction of Di-(4-nitrophenyl)methane with Alkoxide Bases

1972 ◽  
Vol 50 (1) ◽  
pp. 24-30 ◽  
Author(s):  
A. Jarczewski ◽  
K. T. Leffek
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Rate Constants ◽  
Activation Parameters ◽  
Transfer Reactions ◽  
Activation Process ◽  
Proton Transfers ◽  
Proton Transfer Reactions ◽  
Carbon Acids ◽  
Kinetics Of

The second-order rate constants have been measured over a range of temperatures for the proton-transter reactions from di-(4-nitrophenyl)methane to ethoxide, isopropoxide, and t-butoxide ions in solvents consisting of the corresponding alcohols containing 10% toluene by volume. The activation parameters ΔH≠ and ΔS≠ have been calculated and an interpretation of them is given in terms of solvation effects during the activation process. A comparison between the activation parameters for proton transfers and E2 olefin-forming β-elimination reactions is made and discussed with respect to transition state character of the latter reactions.

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