Radiolytic and photolytic production and decay of radicals in adamantane and solutions of 2-methyltetrahydrofuran, 2-methyltetrahydrothiophene, and tetrahydrothiophene in adamantane. Conformation equilibrium of the 2-methyltetrahydrothiophene radical

G Charles Dismukes, John E. Willard

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Abstract

The radicals produced by γ radiolysis of adamantane and adamantane containing 2-methyltetrahydrofuran (MTHF), 2-methyltetrahydrothiophene (MTHT), and tetrahydrothiophene (THT) have been investigated for the purpose of obtaining a better understanding of radical reactions in the adamantane matrix and of clarifying the identity of the radical formed by γ irradiation of pure glassy MTHF. Thermal and photochemical changes in the identity of the radicals produced by γ irradiation of pure adamantane can be induced at 77 K. If solutes are present the adamantyl radicals formed at 77 K are quantitatively replaced by solute radicals on warming, apparently as a result of diffusion of solute molecules to the adamantyl radical centers followed by abstraction of an H atom. For the solutes MTHT, MTHT, and THT, the radicals form only by H abstraction from carbon atoms adjacent to the heteroatom. MTHT forms only the secondary α radical; MTHF forms both the secondary and tertiary α radicals. MTHT radicals in adamantane decay by second-order kinetics with a rate constant of ∼0.17 M-1 s-1 at 295 K. The tertiary and secondary MTHF radicals decay by first-order kinetics with half-lives of ∼1.5 and 3.4 min, respectively, at ∼245 K, accompanied by growth of new radicals. The evidence suggests a unimolecular ring opening followed by H atom abstraction from the matrix. Reversible changes in the ESR spectrum of the MTHT radical in adamantane indicate that the axial methyl conformation is favored relative to the equatorial at 77 K, and that the enthalpy and entropy differences for the two conformations are 1.7 kcal mol-1 and -4.2 cal deg-1, respectively. Analyses of the ESR spectra of the MTHF radicals in adamantane as a function of temperature indicate that the ESR spectrum of the matrix radical in γ-irradiated glassy MTHF is attributable to the tertiary α radical.

Original languageEnglish
Pages (from-to)1435-1445
Number of pages11
JournalJournal of Physical Chemistry
Volume80
Issue number13
Publication statusPublished - 1976

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Adamantane
Paramagnetic resonance
Conformations
Atoms
decay
Irradiation
Radiolysis
Kinetics
Enthalpy
Rate constants
Entropy
Molecules
Carbon
solutes
2-methyltetrahydrofuran
tetrahydrothiophene
Temperature
matrices
atoms

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Radiolytic and photolytic production and decay of radicals in adamantane and solutions of 2-methyltetrahydrofuran, 2-methyltetrahydrothiophene, and tetrahydrothiophene in adamantane. Conformation equilibrium of the 2-methyltetrahydrothiophene radical",
abstract = "The radicals produced by γ radiolysis of adamantane and adamantane containing 2-methyltetrahydrofuran (MTHF), 2-methyltetrahydrothiophene (MTHT), and tetrahydrothiophene (THT) have been investigated for the purpose of obtaining a better understanding of radical reactions in the adamantane matrix and of clarifying the identity of the radical formed by γ irradiation of pure glassy MTHF. Thermal and photochemical changes in the identity of the radicals produced by γ irradiation of pure adamantane can be induced at 77 K. If solutes are present the adamantyl radicals formed at 77 K are quantitatively replaced by solute radicals on warming, apparently as a result of diffusion of solute molecules to the adamantyl radical centers followed by abstraction of an H atom. For the solutes MTHT, MTHT, and THT, the radicals form only by H abstraction from carbon atoms adjacent to the heteroatom. MTHT forms only the secondary α radical; MTHF forms both the secondary and tertiary α radicals. MTHT radicals in adamantane decay by second-order kinetics with a rate constant of ∼0.17 M-1 s-1 at 295 K. The tertiary and secondary MTHF radicals decay by first-order kinetics with half-lives of ∼1.5 and 3.4 min, respectively, at ∼245 K, accompanied by growth of new radicals. The evidence suggests a unimolecular ring opening followed by H atom abstraction from the matrix. Reversible changes in the ESR spectrum of the MTHT radical in adamantane indicate that the axial methyl conformation is favored relative to the equatorial at 77 K, and that the enthalpy and entropy differences for the two conformations are 1.7 kcal mol-1 and -4.2 cal deg-1, respectively. Analyses of the ESR spectra of the MTHF radicals in adamantane as a function of temperature indicate that the ESR spectrum of the matrix radical in γ-irradiated glassy MTHF is attributable to the tertiary α radical.",
author = "Dismukes, {G Charles} and Willard, {John E.}",
year = "1976",
language = "English",
volume = "80",
pages = "1435--1445",
journal = "Journal of Physical Chemistry",
issn = "0022-3654",
publisher = "American Chemical Society",
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T1 - Radiolytic and photolytic production and decay of radicals in adamantane and solutions of 2-methyltetrahydrofuran, 2-methyltetrahydrothiophene, and tetrahydrothiophene in adamantane. Conformation equilibrium of the 2-methyltetrahydrothiophene radical

AU - Dismukes, G Charles

AU - Willard, John E.

PY - 1976

Y1 - 1976

N2 - The radicals produced by γ radiolysis of adamantane and adamantane containing 2-methyltetrahydrofuran (MTHF), 2-methyltetrahydrothiophene (MTHT), and tetrahydrothiophene (THT) have been investigated for the purpose of obtaining a better understanding of radical reactions in the adamantane matrix and of clarifying the identity of the radical formed by γ irradiation of pure glassy MTHF. Thermal and photochemical changes in the identity of the radicals produced by γ irradiation of pure adamantane can be induced at 77 K. If solutes are present the adamantyl radicals formed at 77 K are quantitatively replaced by solute radicals on warming, apparently as a result of diffusion of solute molecules to the adamantyl radical centers followed by abstraction of an H atom. For the solutes MTHT, MTHT, and THT, the radicals form only by H abstraction from carbon atoms adjacent to the heteroatom. MTHT forms only the secondary α radical; MTHF forms both the secondary and tertiary α radicals. MTHT radicals in adamantane decay by second-order kinetics with a rate constant of ∼0.17 M-1 s-1 at 295 K. The tertiary and secondary MTHF radicals decay by first-order kinetics with half-lives of ∼1.5 and 3.4 min, respectively, at ∼245 K, accompanied by growth of new radicals. The evidence suggests a unimolecular ring opening followed by H atom abstraction from the matrix. Reversible changes in the ESR spectrum of the MTHT radical in adamantane indicate that the axial methyl conformation is favored relative to the equatorial at 77 K, and that the enthalpy and entropy differences for the two conformations are 1.7 kcal mol-1 and -4.2 cal deg-1, respectively. Analyses of the ESR spectra of the MTHF radicals in adamantane as a function of temperature indicate that the ESR spectrum of the matrix radical in γ-irradiated glassy MTHF is attributable to the tertiary α radical.

AB - The radicals produced by γ radiolysis of adamantane and adamantane containing 2-methyltetrahydrofuran (MTHF), 2-methyltetrahydrothiophene (MTHT), and tetrahydrothiophene (THT) have been investigated for the purpose of obtaining a better understanding of radical reactions in the adamantane matrix and of clarifying the identity of the radical formed by γ irradiation of pure glassy MTHF. Thermal and photochemical changes in the identity of the radicals produced by γ irradiation of pure adamantane can be induced at 77 K. If solutes are present the adamantyl radicals formed at 77 K are quantitatively replaced by solute radicals on warming, apparently as a result of diffusion of solute molecules to the adamantyl radical centers followed by abstraction of an H atom. For the solutes MTHT, MTHT, and THT, the radicals form only by H abstraction from carbon atoms adjacent to the heteroatom. MTHT forms only the secondary α radical; MTHF forms both the secondary and tertiary α radicals. MTHT radicals in adamantane decay by second-order kinetics with a rate constant of ∼0.17 M-1 s-1 at 295 K. The tertiary and secondary MTHF radicals decay by first-order kinetics with half-lives of ∼1.5 and 3.4 min, respectively, at ∼245 K, accompanied by growth of new radicals. The evidence suggests a unimolecular ring opening followed by H atom abstraction from the matrix. Reversible changes in the ESR spectrum of the MTHT radical in adamantane indicate that the axial methyl conformation is favored relative to the equatorial at 77 K, and that the enthalpy and entropy differences for the two conformations are 1.7 kcal mol-1 and -4.2 cal deg-1, respectively. Analyses of the ESR spectra of the MTHF radicals in adamantane as a function of temperature indicate that the ESR spectrum of the matrix radical in γ-irradiated glassy MTHF is attributable to the tertiary α radical.

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