Thermodynamic measurements on unsubstituted cyclopropenyl radical and anion, and derivatives, by second harmonic alternating current voltammetry of cyclopropenyl cations

Michael R Wasielewski, Ronald Breslow

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Abstract

Cyclopropenyl cation has been reversibly reduced electrochemically to the unsubstituted 3-cyclopropenyl radical, and with two electrons to the unsubstituted 3-cyclopropenyl anion. Reversible thermodynamic reduction potentials for both processes have been determined using second harmonic ac voltammetry. The same technique has been used to determine thermodynamic potentials for the one- and two-electron reduction of triphenylmethyl, cycloheptatrienyl, triphenylcyclopropenyl, trimethylcyclopropenyl, tri-tert-butylcyclopropenyl, and dipropylphenylcyclopropenyl cations. Adsorption effects were detected for two of these cations at a Pt, but not at an Au, electrode. The data were used in thermodynamic sequences to evaluate the basicity of various cyclopropenyl anions; a set of pKa's ranges from +50 to +74. Another thermodynamic sequence was used to evaluate the C-O bond dissociation energy of various cyclopropenols. Two unusual effects emerge: cyclopropenyl radicals are destabilized by alkyl groups, and they also appear to be destabilized relative to unconjugated radicals.

Original languageEnglish
Pages (from-to)4222-4229
Number of pages8
JournalJournal of the American Chemical Society
Volume98
Issue number14
Publication statusPublished - 1976

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Voltammetry
Thermodynamics
Anions
Cations
Negative ions
Positive ions
Derivatives
Electrons
Alkalinity
Adsorption
Electrodes

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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title = "Thermodynamic measurements on unsubstituted cyclopropenyl radical and anion, and derivatives, by second harmonic alternating current voltammetry of cyclopropenyl cations",
abstract = "Cyclopropenyl cation has been reversibly reduced electrochemically to the unsubstituted 3-cyclopropenyl radical, and with two electrons to the unsubstituted 3-cyclopropenyl anion. Reversible thermodynamic reduction potentials for both processes have been determined using second harmonic ac voltammetry. The same technique has been used to determine thermodynamic potentials for the one- and two-electron reduction of triphenylmethyl, cycloheptatrienyl, triphenylcyclopropenyl, trimethylcyclopropenyl, tri-tert-butylcyclopropenyl, and dipropylphenylcyclopropenyl cations. Adsorption effects were detected for two of these cations at a Pt, but not at an Au, electrode. The data were used in thermodynamic sequences to evaluate the basicity of various cyclopropenyl anions; a set of pKa's ranges from +50 to +74. Another thermodynamic sequence was used to evaluate the C-O bond dissociation energy of various cyclopropenols. Two unusual effects emerge: cyclopropenyl radicals are destabilized by alkyl groups, and they also appear to be destabilized relative to unconjugated radicals.",
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T1 - Thermodynamic measurements on unsubstituted cyclopropenyl radical and anion, and derivatives, by second harmonic alternating current voltammetry of cyclopropenyl cations

AU - Wasielewski, Michael R

AU - Breslow, Ronald

PY - 1976

Y1 - 1976

N2 - Cyclopropenyl cation has been reversibly reduced electrochemically to the unsubstituted 3-cyclopropenyl radical, and with two electrons to the unsubstituted 3-cyclopropenyl anion. Reversible thermodynamic reduction potentials for both processes have been determined using second harmonic ac voltammetry. The same technique has been used to determine thermodynamic potentials for the one- and two-electron reduction of triphenylmethyl, cycloheptatrienyl, triphenylcyclopropenyl, trimethylcyclopropenyl, tri-tert-butylcyclopropenyl, and dipropylphenylcyclopropenyl cations. Adsorption effects were detected for two of these cations at a Pt, but not at an Au, electrode. The data were used in thermodynamic sequences to evaluate the basicity of various cyclopropenyl anions; a set of pKa's ranges from +50 to +74. Another thermodynamic sequence was used to evaluate the C-O bond dissociation energy of various cyclopropenols. Two unusual effects emerge: cyclopropenyl radicals are destabilized by alkyl groups, and they also appear to be destabilized relative to unconjugated radicals.

AB - Cyclopropenyl cation has been reversibly reduced electrochemically to the unsubstituted 3-cyclopropenyl radical, and with two electrons to the unsubstituted 3-cyclopropenyl anion. Reversible thermodynamic reduction potentials for both processes have been determined using second harmonic ac voltammetry. The same technique has been used to determine thermodynamic potentials for the one- and two-electron reduction of triphenylmethyl, cycloheptatrienyl, triphenylcyclopropenyl, trimethylcyclopropenyl, tri-tert-butylcyclopropenyl, and dipropylphenylcyclopropenyl cations. Adsorption effects were detected for two of these cations at a Pt, but not at an Au, electrode. The data were used in thermodynamic sequences to evaluate the basicity of various cyclopropenyl anions; a set of pKa's ranges from +50 to +74. Another thermodynamic sequence was used to evaluate the C-O bond dissociation energy of various cyclopropenols. Two unusual effects emerge: cyclopropenyl radicals are destabilized by alkyl groups, and they also appear to be destabilized relative to unconjugated radicals.

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