The α Effect. Aminolysis on a Saturated Carbon Atom

Ōae, Shigeru; Kadoma, Yoshihito; Yano, Yumihiko

doi:10.1246/bcsj.42.1110

Cited by 12 publications

(3 citation statements)

References 12 publications

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“…(2) There are differences in the relative reactivity of α-effect nucleophiles toward carbocations and alkyl halides . The deviations for α-effect nucleophiles reflect the well-known larger effect of nonbonding α-electron pair(s) on nucleophile reactivity toward carbocations than in bimolecular aliphatic substitution reactions. − However, our data provide no additional insight into the origin(s) of the α-effect, which has been the subject of intense, but not entirely conclusive, discussion. ,− …”

Section: Discussionmentioning

confidence: 80%

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

2000

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Second-order rate constants k Nu (M-1 s-1) were determined for addition of a wide range of nucleophiles to the simple quinone methide 4-[bis(trifluoromethyl)methylene]cyclohexa-2,5-dienone (1) to give the nucleophile adduct 1-Nu in water. Equilibrium constants were determined for the overall addition of HBr and HI to 1 to give H-1-Nu, and the data were used to calculate equilibrium constants for the addition of Br- and I- to 1, and to estimate equilibrium constants for the addition of Cl- and AcO-. The values of log k Nu show a linear correlation with the Ritchie nucleophilicity parameter N + with a slope s = 0.92 ± 0.10 that is essentially the same as the electrophile-independent value of 1.0 for highly resonance-stabilized carbocations. Marcus intrinsic barriers Λ of 12.4, 13.9, 15.4, and 19.8 kcal/mol are reported for the addition of I-, Br-, Cl-, and AcO- to 1, respectively. The thermodynamic barriers ΔG° and intrinsic barriers Λ for addition of Br-, Cl-, and AcO- to 1 are 8.4 ± 1.0 and 5.2 ± 0.2 kcal/mol larger, respectively, than the corresponding barriers for addition of these nucleophiles to the triphenylmethyl carbocation. It is concluded that, by the criterion of its chemical reactivity, 1 behaves as a highly resonance-stabilized carbocation. Values of N + = 4.0, 2.2, 1.2 and 0.60, respectively, are reported for I-, Br-, Cl-, and AcO-, which do not form stable adducts to Ritchie electrophiles. The slope of 2.0 (r = 0.98) for the linear correlation between Ritchie (N +) and Swain−Scott (n) nucleophilicity parameters shows that there is substantially greater bonding between the nucleophile and carbon at the transition state for nucleophile addition to sp2-hybridized carbon than for addition to sp3-hybridized carbon. Azide ion and nucleophiles with a nonbonding electron pair(s) at atoms adjacent to the nucleophilic site (α-effect nucleophiles) exhibit significant positive deviations from this correlation.

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Section: Discussionmentioning

confidence: 80%

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

2000

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“…Some further evidence of this is given in Table V, taken from the paper by Oae and coworkers [23]. Thus, although benzyl iodide and p-nitrophenyl acetate are about equally sensitive to basicity, the former does not give an alpha effect with hydrazine, while the latter does.…”

Section: E Some Additional Commentsmentioning

confidence: 89%

“…In an aqueous system, no anomalous reactivity by hydrazine, hydroxylamine, or either of their monomethyl derivatives was seen [22]. Similarly, the alpha effect was reported to be absent from the reactions of hydrazine with methyl, isopropyl, allyl, and benzyl iodides in acetonitrile [23].…”

Section: B Tetrahedral Carbonmentioning

confidence: 92%

The alpha effect. A review

Fina

Edwards

1973

Int J of Chemical Kinetics

164

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Instances of high reactivity (as signaled by a positive Br6nsted deviation) by nucleophiles bearing one or more unshared pairs of electrons on an atom adjacent to the nucleophilic center (the alpha effect) are surveyed in the context of possible explanations for this phenomenon.However, four factors (ground-state destabilization of the nucleophile, transition-state stabilization, solvent effect differences for alpha and nonalpha nucleophiles, and product stability) may be. involved in contributory roles. The response to proton basicity of a substrate is probably not related to its susceptibility to the alpha effect. Carbon electrophiles seem to be receptive to the alpha effect in the order digonal > trigonal > tetrahedral. The inconsistent behavior of alpha nucleophiles makes the prediction of alpha effects rather risky and confirms the complicated nature of nucleophilic substitutions.No single cause appears to account satisfactorily for all the data.

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The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

Buncel

Chuaqui

Wilson

1982

Int J of Chemical Kinetics

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A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p-nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pKa of HOOH in methanol at 25'C as 15.8 f 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH30-+ HzOz i=t CH30H + HOT were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo-first-order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such B corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant kHOO-for the reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio kHOO-/kMeO-= 8.8 f 2.2. This confirms the existence of an (Y effect at saturated carbon in this system.

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The α Effect. Aminolysis on a Saturated Carbon Atom

Cited by 12 publications

References 12 publications

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

The alpha effect. A review

The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

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The α Effect. Aminolysis on a Saturated Carbon Atom

Cited by 12 publications

References 12 publications

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

Structure−Reactivity Relationships and Intrinsic Reaction Barriers for Nucleophile Additions to a Quinone Methide: A Strongly Resonance-Stabilized Carbocation

The alpha effect. A review

The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pKa of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

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Product

Resources

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The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure