Reactions of Charged Substrates. 7. The Methoxymethyl Carbenium Ion Problem. 2. A Semiempirical Study of the Kinetic and Thermodynamic Stabilities of Linear and Cyclic Oxo- and Thiocarbenium Ions Generated from Aldehyde Hydrates, Hemiacetals, Acetals, and Methyl Ribosides and Glucosides

Buckley, Neil; Oppenheimer, Norman J.

doi:10.1021/jo960748t

Cited by 21 publications

(39 citation statements)

References 43 publications

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“…7a. This diagram, which is similar to those suggested for general acid-and base-catalyzed breakdown (or formation) of hemiacetals (12)(13)(14)(15)(16)(17)(18)(19)(20) This mechanism is energetically more favorable than the two stepwise mechanisms because the formation of the h or i high energy intermediates is avoided. In a way similar to that described previously in the case of hemiacetal breakdown (20), the standard Gibbs free energy differences, G h 0 -G r 0 , G i 0 -G r 0 , and G p 0 -G r 0 between corners h, i, and p, and starting materials can be calculated by combining the free energy changes for α-EA formation, iminium ion and α-EA protonation, carboxylic acid dissociation, and methanol autoprotolysis.…”

Section: More O'ferrall -Jencks Diagramsupporting

confidence: 80%

“…Studies of general acid-and base-catalyzed hemiacetal formation and hydrolysis have played an important role in the development of the theories dealing with concerted mechanisms (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). In view of the analogy of Schiff bases (and corresponding iminium ions) with carbonyl compounds, we thought that a general acid-catalyzed mechanism according to Scheme 2 can occur for alcohol addition to the former compounds.…”

Section: Introductionmentioning

confidence: 99%

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General acid-catalyzed addition of methanol to (E)-N-benzylideneanilines

Bennour¹,

Toullec²

1999

Can. J. Chem.

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The reaction of equilibrium addition of methanol (α-amino ether formation) to benzylideneanilines (C 6 H 5 CHϭNC 6 H 4 Y, with Y = H (1a), 3-Cl (1b), 3-NO 2 (1c), 4-CN (1d), and 4-NO 2 (1e)) in methanol is shown to be general acid-catalyzed in carboxylic acid buffers. The mechanism involves fast iminium ion formation followed by base-assisted addition of methanol. The α Brønsted exponents are in the 0.67-0.88 range, and α increases with the electron-withdrawing ability of Y. The same mechanism is valid for MeOH 2 + -catalysis, meaning that two solvent molecules are involved in the addition process, one of them playing the role of base. The equilibrium constant, K, is increased by electron-withdrawing substituents, log K depending linearly on the σ -substituent parameters. The substituent effects on the forward and reverse catalytic rate constants are analyzed by means of the log k = ρ n σ n + ρ r (σ --σ n ) + constant (Young-Jencks) equation. For carboxylic acid catalysis, the ρ n and ρ r parameters are in keeping with ca. half C-O bond forming or breaking at the transition state. The catalytic rate constants and α exponent for elimination of ClCH 2 CH 2 OH in methanol from the C 6 H 5 CH(OCH 2 CH 2 Cl)NH(4-CNC 6 H 4 ) chloroethyl adduct are compared with those for the elimination of methanol from C 6 H 5 CH(OCH 3 )NH(4-CNC 6 H 4 ). The chloromethyl group makes the reaction slower and α lower. This indicates that proton transfer is a little ahead of C-O bond cleavage at the transition state. Y substituent effects, α values, and the effects of the CH 2 Cl group are interpreted on the basis of a More O'Ferrall -Jencks diagram.

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Section: More O'ferrall -Jencks Diagramsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

General acid-catalyzed addition of methanol to (E)-N-benzylideneanilines

Bennour¹,

Toullec²

1999

Can. J. Chem.

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“…At this stage it is revealing to compare this scenario to what was observed in gas phase calculations [18] where the transition state of protonated methyl b-d-glucopyranoside was found to feature a stabilizing intramolecular interaction of the protonated O m by O 6 instead of an intermolecular stabilization due to solvent molecules. In the light of the present "wet chemistry" results this intramolecular stabilization looks like an artefact-when compared with the situation in solution-that is caused by the lack of solvent.…”

mentioning

confidence: 77%

“…Previous theoretical treatments have investigated aspects of such hydrolysis reactions by using quantum chemical gas phase or continuum solvation methods [17][18][19][20][21] where the conformation of exocyclic substituents such as the C 6 …”

Section: Introductionmentioning

confidence: 99%

Aspects of Glycosidic Bond Formation in Aqueous Solution: Chemical Bonding and the Role of Water

Stubbs

Marx

2005

Chemistry A European J

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A model of the specific acid-catalyzed glycosidic bond formation in liquid water at ambient conditions is studied based on constrained Car-Parrinello ab initio molecular dynamics. Specifically the reaction of alpha-D-glucopyranose and methanol is found to proceed by a D(N)A(N) mechanism. The D(N) step consists of a concerted protonation of the O(1) hydroxyl leaving group; this process results in the breaking of the C(1)-O(1) bond, and oxocarbenium ion formation involving C(1)=O(5). The second step, A(N), is the formation of the C(1)-O(m) glycosidic bond, deprotonation of the methanol hydroxyl group O(m)H(m), and re-formation of the C(1)-O(5) single bond. A focus of this study is the analysis of the electronic structure during this condensed phase reaction relying on both Boys/Wannier localized orbitals and the electron localization function ELF. This analysis allows the clear elucidation of the chemical bonding features of the intermediate bracketed by the D(N) and A(N) steps, which is a non-solvent equilibrated oxocarbenium cation. Most interestingly, it is found that the oxygen in the pyranose ring becomes "desolvated" upon double bond/oxocarbenium formation, whereas it is engaged in the hydrogen-bonded water network before and after this period. This demonstrates that hydrogen bonding and thus the aqueous solvent play an active role in this reaction implying that microsolvation studies in the gas phase, both theoretical and experimental, might lead to qualitatively different reaction mechanisms compared to solution.

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“…8 Computational studies have been performed on acid catalysis, specifically Brønsted acids. 3,9,10 Ozment et al 9 investigated protonation of 3-acetyltriazene to look at the decomposition of triazenes, with predicted bond cleavage based on the protonation site. Where appropriate, comparisons of the present calculations with previous calculations will be made.…”

Section: Introductionmentioning

confidence: 99%

Density Functional Investigation of Melamine−Formaldehyde Cross-Linking Agents. 1. Partially Substituted Melamine

Benson

2003

Ind. Eng. Chem. Res.

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Computational modeling has been performed on the cross-linking mechanism of partially substituted melamine reacting with poly(vinyl alcohol). Ab initio calculations were performed with density functional theory employing the BLYP functional and double numerical DND basis set. The mechanism, general acid catalysis, has been modeled with respect to structures, protonation, and reaction with a polymer. Protonation of the oxygen is required initially, followed by liberation of methanol. The reaction can take one of two pathways after methanol liberation. The conjugate base of the weak acid can abstract a proton, generating a Schiff-base intermediate.The O-H on the polymer then adds to the C-N double bond, producing the polymer-melamine bond. The alternative is that the polymer adds to the charged melamine, using the specific acid catalysis mechanism. After polymer addition, the proton is abstracted, producing the product.

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Reactions of Charged Substrates. 7. The Methoxymethyl Carbenium Ion Problem. 2. A Semiempirical Study of the Kinetic and Thermodynamic Stabilities of Linear and Cyclic Oxo- and Thiocarbenium Ions Generated from Aldehyde Hydrates, Hemiacetals, Acetals, and Methyl Ribosides and Glucosides

Cited by 21 publications

References 43 publications

General acid-catalyzed addition of methanol to (E)-N-benzylideneanilines

General acid-catalyzed addition of methanol to (E)-N-benzylideneanilines

Aspects of Glycosidic Bond Formation in Aqueous Solution: Chemical Bonding and the Role of Water

Density Functional Investigation of Melamine−Formaldehyde Cross-Linking Agents. 1. Partially Substituted Melamine

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