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. [77 and 295/sup 0/K]

Journal Article · Thu Jun 17 04:00:00 EDT 1976 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100554a010· OSTI ID:7355038

Dismukes, G C; Willard, J E

The radicals produced by ..gamma.. 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 ..gamma.. irradiation of pure glassy MTHF. Thermal and photochemical changes in the identity of the radicals produced by ..gamma.. irradiation of pure adamantane can be induced at 77/sup 0/K. If solutes are present, the adamantyl radicals formed at 77/sup 0/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 MTHF, MTHT, and THT, the radicals form only by H abstraction from carbon atoms adjacent to the heteroatom. MTHT forms only the secondary ..cap alpha.. radical; MTHF forms both the secondary and tertiary ..cap alpha.. radicals. MTHT radicals in adamantane decay by second-order kinetics with a rate constant of approximately 0.17 M/sup -1/ s/sup -1/ at 295/sup 0/K. The tertiary and secondary MTHF radicals decay by first-order kinetics with half-lives of approximately 1.5 and 3.4 min, respectively, at approximately 245/sup 0/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/sup 0/K, and that the enthalpy and entropy differences for the two conformations are 1.7 kcal mol/sup -1/ and --4.2 cal deg/sup -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 ..gamma..-irradiated glassy MTHF is attributable to the tertiary ..cap alpha.. radical.

• Research Organization: Univ. of Wisconsin, Madison
• OSTI ID: 7355038
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 80:13; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400500 -- Photochemistry
400600* -- Radiation Chemistry
ADAMANTANE
ALKANES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CYCLOALKANES
DECOMPOSITION
ELECTROMAGNETIC RADIATION
FURANS
GAMMA RADIATION
GLASS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
IONIZING RADIATIONS
LOW TEMPERATURE
MEDIUM TEMPERATURE
MTHF
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADIOLYSIS