Solvation Changes Accompanying Proton Transfer from a Carbon Acid to Alkoxide Bases As Revealed by Kinetic Isotope Effects

Thomas E. Casamassina; W. Phillip Huskey

doi:10.1021/ja00054a003

Solvation Changes Accompanying Proton Transfer from a Carbon Acid to Alkoxide Bases As Revealed by Kinetic Isotope Effects

Thomas E. Casamassina, W. Phillip Huskey

Rutgers Newark, Chemistry

Research output: Contribution to journal › Article › peer-review

22 Scopus citations

Abstract

Primary hydrogen isotope effects are reported for the elimination of 4-nitrophenol from 4-(4-nitrophenoxy)-2-butanone in methanolic methoxide at 20 °C and in aqueous hydroxide at 25 °C. The isotope effects do not change significantly when the isotopic composition of the solvents is changed: (k_H/k_D)_MeOH = 6.48 ± 0.22, (k_H/k_D)_MeOD = 6.40 ± 0.24; and (k_H/k_D)_HOH = 7.54 ± 0.11, (k_H/k_D)_DOD = 7.48 ± 0.21. Kinetic solvent isotope effects (using the undeuterated substrate) are k_MeOD/k_MeOH = 2.195 ± 0.064 and k_DOD/k_HOH = 1.526 ± 0.029. The experimental results are compared with model vibrational analysis calculations and about 60 literature examples of related solvent isotope effects on proton-transfer rates. The observations of primary hydrogen isotope effects that are unchanged upon isotopic substitution in protonic sites of the solvent were used to conclude that solvent reorganization is not coupled to proton transfer in the reaction coordinate.

Original language	English (US)
Pages (from-to)	14-20
Number of pages	7
Journal	Journal of the American Chemical Society
Volume	115
Issue number	1
DOIs	https://doi.org/10.1021/ja00054a003
State	Published - Jan 1 1993

All Science Journal Classification (ASJC) codes

Catalysis
Chemistry(all)
Biochemistry
Colloid and Surface Chemistry

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title = "Solvation Changes Accompanying Proton Transfer from a Carbon Acid to Alkoxide Bases As Revealed by Kinetic Isotope Effects",

abstract = "Primary hydrogen isotope effects are reported for the elimination of 4-nitrophenol from 4-(4-nitrophenoxy)-2-butanone in methanolic methoxide at 20 °C and in aqueous hydroxide at 25 °C. The isotope effects do not change significantly when the isotopic composition of the solvents is changed: (kH/kD)MeOH = 6.48 ± 0.22, (kH/kD)MeOD = 6.40 ± 0.24; and (kH/kD)HOH = 7.54 ± 0.11, (kH/kD)DOD = 7.48 ± 0.21. Kinetic solvent isotope effects (using the undeuterated substrate) are kMeOD/kMeOH = 2.195 ± 0.064 and kDOD/kHOH = 1.526 ± 0.029. The experimental results are compared with model vibrational analysis calculations and about 60 literature examples of related solvent isotope effects on proton-transfer rates. The observations of primary hydrogen isotope effects that are unchanged upon isotopic substitution in protonic sites of the solvent were used to conclude that solvent reorganization is not coupled to proton transfer in the reaction coordinate.",

author = "Casamassina, {Thomas E.} and Huskey, {W. Phillip}",

year = "1993",

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AU - Casamassina, Thomas E.

AU - Huskey, W. Phillip

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Y1 - 1993/1/1

N2 - Primary hydrogen isotope effects are reported for the elimination of 4-nitrophenol from 4-(4-nitrophenoxy)-2-butanone in methanolic methoxide at 20 °C and in aqueous hydroxide at 25 °C. The isotope effects do not change significantly when the isotopic composition of the solvents is changed: (kH/kD)MeOH = 6.48 ± 0.22, (kH/kD)MeOD = 6.40 ± 0.24; and (kH/kD)HOH = 7.54 ± 0.11, (kH/kD)DOD = 7.48 ± 0.21. Kinetic solvent isotope effects (using the undeuterated substrate) are kMeOD/kMeOH = 2.195 ± 0.064 and kDOD/kHOH = 1.526 ± 0.029. The experimental results are compared with model vibrational analysis calculations and about 60 literature examples of related solvent isotope effects on proton-transfer rates. The observations of primary hydrogen isotope effects that are unchanged upon isotopic substitution in protonic sites of the solvent were used to conclude that solvent reorganization is not coupled to proton transfer in the reaction coordinate.

AB - Primary hydrogen isotope effects are reported for the elimination of 4-nitrophenol from 4-(4-nitrophenoxy)-2-butanone in methanolic methoxide at 20 °C and in aqueous hydroxide at 25 °C. The isotope effects do not change significantly when the isotopic composition of the solvents is changed: (kH/kD)MeOH = 6.48 ± 0.22, (kH/kD)MeOD = 6.40 ± 0.24; and (kH/kD)HOH = 7.54 ± 0.11, (kH/kD)DOD = 7.48 ± 0.21. Kinetic solvent isotope effects (using the undeuterated substrate) are kMeOD/kMeOH = 2.195 ± 0.064 and kDOD/kHOH = 1.526 ± 0.029. The experimental results are compared with model vibrational analysis calculations and about 60 literature examples of related solvent isotope effects on proton-transfer rates. The observations of primary hydrogen isotope effects that are unchanged upon isotopic substitution in protonic sites of the solvent were used to conclude that solvent reorganization is not coupled to proton transfer in the reaction coordinate.

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Solvation Changes Accompanying Proton Transfer from a Carbon Acid to Alkoxide Bases As Revealed by Kinetic Isotope Effects

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