Steric effects on reaction rates. XI. Solvolysis of tertiary carbon substrates rationalized by molecular mechanics calculations

Müller, Paul; Mareda, Jiri

doi:10.1002/jcc.540100702

Cited by 14 publications

(4 citation statements)

References 22 publications

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“…2,4 In addition, the tertiary neopentyl derivative 5, which should be far less subject to nucleophilic solvent assistance, 13,14 solvolyses also at an enhanced rate, although the deviation is much less pronounced than in the case of tert-butyl (9). The rate ratio for solvolysis of 1-adamantyl vs. tert-butyl (2-methyl-2-propyl) derivatives varies from ca 1:5000 in EtOH 10 to 1600 in MeOH 11 and 1:2.4 12 in 97% aqueous HFIP.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 However, since the calculations were empirical, and since the forcefields used were adjusted such as to provide an optimum correlation with the experimental data, the significance of the calculations is questionable. Early empirical force-field calculations have been used to rationalize the structural effects on the rate constants of solvolysis in terms of strain changes between the bridgehead compound and the developing carbenium ion, which was assumed to be close to the transition state of the reaction in terms of energy and structure.…”

Section: Introductionmentioning

confidence: 99%

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Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

Müller

Rossier

Abboud

2000

J. Phys. Org. Chem.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

Müller

Rossier

Abboud

2000

J. Phys. Org. Chem.

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“…It was found that all of the rate constants established by Bentley could be accommodated with the calculated strain changes by means of a single correlation [7]. Tertiary derivatives of general structure, such as acyclic, mono-, and polycyclic compounds fit the same correlation, although the quality of the plot is significantly below that observed for the bridgehead derivatives alone [8].…”

mentioning

confidence: 99%

“…A series of 24 bridgehead or rigid tertiary bridgehead derivatives evenly distributed over the entire rate range was selected, and the steric energy difference dE,,(R+ -RBr) was calculated with the UNICAT 4 carbenium ion force field [7] (cf. Appendix) and correlated with the solvolytic reactivity under standard conditions [4] [5] [8] by means of Eqn. I :…”

mentioning

confidence: 99%

Steric Effects on Reaction Rates. Part XII. Force‐Field Calculations for the Solvolysis of Cyclobutyl and Tricyclyl Derivatives

Müller

Milin

1991

Helvetica Chimica Acta

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(1 6.VIII.91) Force-field parameters have been developed for the molecular-mechanics calculation of tertiary carbenium ions with tricyclane structure, for tertiary cyclobutyl and cubyl cations. The cyclobutyl parameters are also applicable to tertiary 7-norbornyl cations. Satisfactory plots are obtained for correlation of the rates of solvolysis with the differences in steric energies between carbenium ions and the corresponding bromides.Introduction. -Bridgehead derivatives constitute a mechanistically homogeneous series in solvolysis reactions. Their solvolytic reactivity has been investigated systematically by Schleyer and coworkers [I-31. The reactions were found to be dominated by strain changes upon change of hybridization of the reacting C-atom from sp3 to sp2 in going to the transition state. These strain changes were calculated by molecular mechanics [3], and they were successfully correlated with the experimental rate constants (log k ) for solvolysis of bridgehead chlorides, bromides, p -toluenesulfonates, and trifluoromethane sulfonates. The solvolytic reactivity of bridgehead derivatives varies enormously with the structure of the substrate, and it is impossible to measure the rate constants with one and the same leaving group and under identical experimental conditions. For quantitative strain-reactivity correlations, a uniform reactivity scale is a prerequisite. Such a reactivity scale has been set up. Bentley and Roberts [4] have critically established rate constants for several bridgehead derivatives with different leaving groups. It was found that relative rate constants in the series are almost independent from the leaving group and the solvent, and subsequently to this observation, correction factors for solvent and leaving group changes (chlorides, bromides, p-toluenesulfonates, and trifluoromethane sulfonates) have been proposed. A reactivity scale for standard conditions (TsO leaving group solvolyzing at 70°in 80 % aq. EtOH) spanning a rate range of 22 log units was established. Similarly, conversion factors for p -nitrobenzoate solvolysis and for acid-catalyzed dehydration of tertiary alcohols in the bridgehead and nonbridgehead series have been determined by using linear free-energy relationships [5]. The extrapolated rate constants, when taken from different conditions, agree in general within 0.5 log units.The original strain-reactivity calculations for bridgehead derivatives were carried out with a preliminary force field which was later abandoned. More recently the strain calculations of Schleyer have been repeated with a carbenium ion force field similar

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A new method for empirical force field calculations on localized and delocalized carbocations

1996

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A new empirical force field method for localized and delocalized carbocations is described. Additional geometry parameters for carbocations were added to Allinger's MMP2 molecular mechanics program, which can treat delocalized π‐systems. The effect of hyperconjugation in carbocations is introduced via a quantum chemical term into force field calculations for the first time. The calculated heats of formation are in excellent agreement with a wide range of experimental data; the largest deviations are about 3.5 kcal/mol. The calculated structures agree very well with those computed at correlated ab initio levels (MP2(full)/6‐31G*). The relative energies and geometries of different conformations of representative carbocations also were in good agreement with MP4/6‐31G*//MP2(full)/6‐31G* results. © 1996 by John Wiley & Sons, Inc.

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Steric effects on reaction rates. XI. Solvolysis of tertiary carbon substrates rationalized by molecular mechanics calculations

Cited by 14 publications

References 22 publications

Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

Gas-phase stability of tertiary carbenium ions and rates of solvolysis of tertiary derivatives

Steric Effects on Reaction Rates. Part XII. Force‐Field Calculations for the Solvolysis of Cyclobutyl and Tricyclyl Derivatives

A new method for empirical force field calculations on localized and delocalized carbocations

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