A simple theory for predicting the effects of substituent changes on transition-state geometry

Thornton, Edward R.

doi:10.1021/ja00988a020

Cited by 205 publications

(119 citation statements)

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“…62 In general, as the stability of the carbocations on the reaction coordinate increases, the transition state is moved closer to the reactants and the magnitude of the solvent isotope effect decreases. 52,63,64 Since the highly anionic 1 is able to greatly stabilize cationic guest molecules, the observed shift in mechanism from A-1 to A-S E 2 upon encapsulation may be a direct effect of the preference of monocationic guests to be encapsulated in 1.…”

Section: Resultsmentioning

confidence: 99%

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

et al. 2009

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A water-soluble self-assembled supramolecular host molecule catalyzes the hydrolysis of orthoformates in basic solution. Comparison of the rate constants of the catalyzed and uncatalyzed reactions for hydrolysis displays rate accelerations of up to 3900 for tri-n-propyl orthoformate. Kinetic analysis shows that the mechanism of hydrolysis with the supramolecular host obeys the Michaelis-Menten model.Mechanistic studies, including 13 C-labeling experiments, revealed that the resting state of the catalytic system is the neutral substrate encapsulated in the host. Activation parameters for the k cat step of the reaction revealed that upon encapsulation in the assembly, the entropy of activation becomes more negative in contrast to the uncatalyzed reaction. Furthermore, solvent isotope effects reveal a normal k(H 2 O)/k(D 2 O) = 1.6, confirming that proton transfer is occurring in the transition state and is rate limiting in the catalyzed reaction. In comparison to the uncatalyzed reaction, which operates by an A-1 mechanism in which the decomposition of the protonated substrate is rate limiting, the encapsulated reaction proceeds through an A-S E 2 mechanism in which proton transfer from protonated water to the substrate is rate limiting.

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Section: Resultsmentioning

confidence: 99%

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

et al. 2009

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“…Once the actual transition state structures had been determined, the effect of changing a substituent at the a carbon could be compared with the theoretical predictions based on Thornton's reacting bond rule (50) and More O'Ferrall's energy surface (6,51). According to Thornton's rule, the overall effect of a S,2 reaction is comprised of the substituent effect on the perpendicular and the parallel vibrations of the transition state.…”

Section: Comparison Of the Experimental Results And Theoretical Predimentioning

confidence: 99%

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of S_N2 transition states

Westaway¹,

Waszczylo²

1982

Can. J. Chem.

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Kinetic studies, secondary α-deuterium kinetic isotope effects, primary chlorine kinetic isotope effects (1), Hammett ρ values determined by changing the substituent in the nucleophile, and activation parameters have been used to determine the detailed (relative) structures of the transition states for the SN2 reactions between para-substituted benzyl chlorides and thiophenoxide ion. A rationale for the U-shaped Hammett ρ plots observed when para-substituted benzyl compounds react with negatively charged nucleophiles is also presented.

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“…pK a = 47 -34 n CO (2) Calculation of pK a (TS) should allow the estimation of n ‡ CO , which in turn leads to the calculation of f ν ‡ , or the corresponding value for the stretching frequency of the carbonyl oscillator in the transition state.…”

Section: Modelmentioning

confidence: 99%

“…2 Reasonable atom connectivities, geometry and force field are the goals to achieve for the description of these transient molecular entities. The first two features are based on chemical intuition or isotopic labelling experiments, whereas the third comes from the molecular analysis of kinetic measurements or from theoretical calculations.…”

Section: Introductionmentioning

confidence: 99%

“…Major electronic effects are expected to operate through the relatively weak and polarisable bonds of the TS complex, which are significantly being perturbed during the course of the reaction. 2 The strong bonds in reactant molecules and those "non-reacting" bonds in the TS complex are less likely to be perturbed by the action of substituents. As a way of comparison, this Hammett ρ parameter is certainly larger than ρ = 0.47, for the ionisation of ArCH 2 -CO 2 H in water solvent at 25 °C.…”

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confidence: 99%

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The transition-state acidity and carbonyl stretching frequency in ester hydrolysis. A substituent-effect approach

Mata‐Segreda

2003

Arkivoc

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The acidity of the transition-state complex in the acid-catalysed hydrolysis of esters increases by the effect of electron-withdrawing groups in either the acyl or alkyl moieties. From the pK a of 13 transition-state complexes, the vibrational frequency of the carbonyl oscillator in the transition state was found equal to 1300 ± 100 cm -1 , the same as in the cases of saponification of methyl formate and the methoxide-catalysed methanolysis of p-bromophenyl benzoate. This suggests that the transition-state complexes of both lyonium and lyate catalysed reactions share similar structural features.

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A simple theory for predicting the effects of substituent changes on transition-state geometry

Cited by 205 publications

References 0 publications

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of S_N2 transition states

The transition-state acidity and carbonyl stretching frequency in ester hydrolysis. A substituent-effect approach

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A simple theory for predicting the effects of substituent changes on transition-state geometry

Cited by 205 publications

References 0 publications

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of SN2 transition states

The transition-state acidity and carbonyl stretching frequency in ester hydrolysis. A substituent-effect approach

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Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of S_N2 transition states