Intrinsic barriers in nucleophilic displacements

Pellerite, Mark J.; Brauman, John I.

doi:10.1021/ja00539a003

Cited by 189 publications

(93 citation statements)

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“…The energy then increases as the reaction proceeds to the transition state and this transition state has a lower electronic energy than the reactants [16]. These theoretical results are in agreement with the experimental ones [5,6] which may be represented by potential-energy profiles with a double minimum [3,40].…”

Section: S N 2 Reactions Through Ab Initio Calculationssupporting

confidence: 87%

Theoretical approach of the chemical reactivity: The S_N2 reaction

Serre

1984

Int J of Quantum Chemistry

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Section: S N 2 Reactions Through Ab Initio Calculationssupporting

confidence: 87%

Theoretical approach of the chemical reactivity: The S_N2 reaction

Serre

1984

Int J of Quantum Chemistry

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“…[7,18] This uncertainty, due to the lack of solvation in the theoretical approach, was demonstrated when research indicated that the solvation energy for simple organic reactions was large and that the free energies of activation including solvent were very different from those calculated in the gas phase. This solvation problem was also demonstrated by the work of Bohme and co-workers [19] and others [20,21] who showed that the reaction coordinate was different for S N 2 reactions in the gas phase and in solution. Another problem that plagued the theoretical approach to determining transition-state structure was that only the largest computers were able to calculate the structure of even medium-sized molecules accurately.…”

Section: Introductionmentioning

confidence: 74%

“…This was done so that the enthalpy of activation could also be used to assess the results from the different theoretical methods in which solvation was included in the calculations. The activation parameters were not calculated for the gas-phase models in which the reaction coordinate [20,21] and the activation parameters are very different from those in solution. [19] The theoretical models: Forty-two different theoretical methods have been used to calculate the structure of the transition state and the experimental KIEs for the ethyl chloride ± cyanide ion S N 2 reaction for an S N 2 reaction.…”

mentioning

confidence: 99%

Experimental and Theoretical Multiple Kinetic Isotope Effects for an S_N2 Reaction. An Attempt to Determine Transition‐State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects

Fang

Gao

Ryberg

et al. 2003

Chemistry A European J

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The secondary alpha-deuterium, the secondary beta-deuterium, the chlorine leaving-group, the nucleophile secondary nitrogen, the nucleophile (12)C/(13)C carbon, and the (11)C/(14)C alpha-carbon kinetic isotope effects (KIEs) and activation parameters have been measured for the S(N)2 reaction between tetrabutylammonium cyanide and ethyl chloride in DMSO at 30 degrees C. Then, thirty-nine readily available different theoretical methods, both including and excluding solvent, were used to calculate the structure of the transition state, the activation energy, and the kinetic isotope effects for the reaction. A comparison of the experimental and theoretical results by using semiempirical, ab initio, and density functional theory methods has shown that the density functional methods are most successful in calculating the experimental isotope effects. With two exceptions, including solvent in the calculation does not improve the fit with the experimental KIEs. Finally, none of the transition states and force constants obtained from the theoretical methods was able to predict all six of the KIEs found by experiment. Moreover, none of the calculated transition structures, which are all early and loose, agree with the late (product-like) transition-state structure suggested by interpreting the experimental KIEs.

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“…In Equation (12), k o refers to the rate of a standard reaction, and k is the rate of the reaction of the nucleophile under consideration. The parameter s is the sensitivity of the given substrate.…”

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confidence: 99%

Nucleophilicity—Periodic Trends and Connection to Basicity

Uggerud

2006

Chemistry A European J

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The potential energy profiles of 18 identity S(N)2 reactions have been estimated by using G2-type quantum-chemical calculations. The reactions are: X- + CH3-X --> X-CH3 + X- and XH + CH3-XH+ --> +HX-CH3 + XH (X = NH2, OH, F, PH2, SH, Cl, AsH2, SeH, Br). Despite the charge difference, the barrier heights and the geometrical requirements upon going from the reactant to the transition structure are surprisingly similar for X- and XH. The barrier heights decrease on going from left to right in the periodic table, and increasing ionization energy (of X- and XH) is correlated with decreasing barrier. The observed trends are explained in terms of substrates with stronger electrostatic character giving rise to lower energetic barriers due to decreased electron repulsion in the transition structure. On the basis of this study, the relationship between the kinetic concept of nucleophilicity and the thermodynamic concept of basicity has been analyzed and clarified. Since the trends in intrinsic nucleophilicity (only defined for identity reactions) and basicity are opposite, overall nucleophilicity (defined for any reaction) will be determined by the relative contribution of the two factors. Only for strongly exothermic reactions will basicity and nucleophilicity be matching.

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Intrinsic barriers in nucleophilic displacements

Abstract: equation,26 and HSAB theory20 have all been used in attempts to correlate reactivity with structural or thermodynamic properties. Success of these correlations is rather limited, as absolute and even relative rates of SN2 reactions have been found to be highly solvent (2) (a) Swain, C.

Cited by 189 publications

References 5 publications

Theoretical approach of the chemical reactivity: The S_N2 reaction

Theoretical approach of the chemical reactivity: The S_N2 reaction

Experimental and Theoretical Multiple Kinetic Isotope Effects for an S_N2 Reaction. An Attempt to Determine Transition‐State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects

Nucleophilicity—Periodic Trends and Connection to Basicity

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Intrinsic barriers in nucleophilic displacements

Abstract: equation,26 and HSAB theory20 have all been used in attempts to correlate reactivity with structural or thermodynamic properties. Success of these correlations is rather limited, as absolute and even relative rates of SN2 reactions have been found to be highly solvent (2) (a) Swain, C.

Cited by 189 publications

References 5 publications

Theoretical approach of the chemical reactivity: The SN2 reaction

Theoretical approach of the chemical reactivity: The SN2 reaction

Experimental and Theoretical Multiple Kinetic Isotope Effects for an SN2 Reaction. An Attempt to Determine Transition‐State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects

Nucleophilicity—Periodic Trends and Connection to Basicity

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Product

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Theoretical approach of the chemical reactivity: The S_N2 reaction

Theoretical approach of the chemical reactivity: The S_N2 reaction

Experimental and Theoretical Multiple Kinetic Isotope Effects for an S_N2 Reaction. An Attempt to Determine Transition‐State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects