Kinetics and CIDEP of radicals during photoreduction of acetone with 2-propanol by effect modulated ESR spectroscopy

ESR spectroscopy with modulated radical initiation is used to analyze quantitatively chemical lifetimes and CIDEP enhancements of 2-propyl-2-ol radicals, formed by photoreduction of acetone with 2-propanol in aqueous solution at T = 16°C. The bimolecular termination rate constant of the radicals is found to be diffusion controlled and to depend on the hyperfine state as a consequence of T₀---S mixing in F-pairs. CIDEP enhancements built up in geminate and in F-pairs are separated. Their relative dependence on the hyperfine state agrees with microscopic theory, which however, fails to reproduce the absolute enhancements by a factor of 4. The polarizations indicate equal reactivities towards photoreduction for the three sublevels of the ³nπ* state of acetone, and conservation of the electron spin polarization upon radical formation. The initial separation of the species in the geminate pair is found to lie within the strong exchange region, since geminate and F-pairs show equal RPM polarizations. The CIDEP enhancements limit the rate constant k₂₂ for abstraction of the hydroxylic hydrogen of 2-propanol by ³nπ* acetone to k₂₂ < 10⁵ dm³ mol⁻¹ s ⁻¹.     

An ESR study of polyisobutylene radicals produced by γ-irradiation at 77 K

An electron spin resonance (ESR) study has been made of radicals trapped in polyisobutylene irradiated at 77 K. It is concluded that only the ? C(Me)₂? CH? radical remains after heat treatment above 213 K. This radical shows a very sharp doublet ESR spectrum with hyperfine splitting of about 2.2 mT. A broad doublet ESR spectrum observed without warming, which was previously assigned as ? C(Me)₂? CH? is explained as a mixture of a doublet and a triplet due to the ? C(Me)₂? CH? and radicals. γ-irradiation at 77 K produces these major radical components and other carbon radicals as minor species. It has also been found that a conversion of other radicals into ? C(Me)₂? CH? occurs without decay on annealing below 183 K. Heating in the range 183–213 K causes both conversion and decay of the radicals. On annealing above 213 K, only decay occurs. The ESR spectra of polyisobutylene radicals are easily saturated by microwave power even at 1.6 μW. The mechanism of radiolysis for polyisobutylene is briefly discussed.     

Addition of radicals to quinones—I. ESR study of addition products from chloroquinones and free radicals

The mechanism of addition reactions of radicals formed during thermal decomposition of benzoyl peroxide with various chloro-substituted p-benzoquinones has been studied by the ESR technique in various solvents. The ESR spectra of the intermediate radicals show that addition occurs at the carbonyl oxygen. The important role of charge-transfer complexes in the reaction has been established. For strong CT complexes, the quinone molecule reacts with radicals derived from the solvent.     

Confirmation of the cation radicals of hexamethylethane and hexamethyldisilane by ESR and other spectroscopy

Unambiguous ESR spectra of cation radicals of hexamethylethane and hexamethyldisilane were obtained for γ-irradiated solutions in CCl₃F at 77 and 140 K. INDO calculations, optical measurements, and comparison with photoelectron spectra are consistent with the observed ESR spectra.     

Chalcogenide Derivatives of the seco‐Cubane [Sn3(μ2‐NHtBu)2(μ2‐NtBu)(μ3‐NtBu)]

A series of monochalcogenide derivatives of the seco‐cubane [Sn₃(μ₂‐NHtBu)₂(μ₂‐NtBu)(μ₃‐NtBu)] has been prepared and characterized by NMR and X‐ray crystallographic studies. These complexes exhibit different tin‐chalcogen bonding modes. In the case of the monotelluride, a terminal Sn=Te bond was observed in solution and in the solid state, whereas for the monosulfide, a μ₂ bridging mode was adopted by the sulfur atoms. The monoselenide was found to employ both bonding modes in solution, although only the terminal Sn=Se bonding mode was structurally characterized. The complexes undergo chalcogen exchange between tin atoms in solution, and this process was studied by variable temperature NMR.     

Electrophilic attacks on μ3-bridging acetyl in a triiron carbonyl cluster; C---O bond cleavage to give μ3-ethylidyne and μ-methoxo groups

The triiron carbonyl cluster anion, [Fe₃(CO)₉(μ₃-CH₃CO)]⁻ react with fluoroboric acid to give the neutral cluster Fe₃(CO)₉(μ-H)(μ₃-CH₃CO). Methylfluorosulphate reacts to give the compound Fe₃(CO)₉(μ₃-CCH₃) (μ₃-OCH₃) in which the μ₃-acetyl group has undergone stoichiometric C---O bond cleavage.     

ESR spectroscopic investigation of steric and polar factors in the addition of radicals to unsaturated compounds

The rate constants of the addition of CCl₃CH₂ClCH₃(R⁶) radicals to -methyl-styrene, styrene, methyl methacrylate, methyl acrylate, and acrylonitrile and of CCl₃CH₂(CH₃)₂(R⁷) radicals to styrene, methyl acrylate, and acrylonitrile were determined by ESR spectroscopy. It was shown that the radicals R⁶ and R⁷ possess approximately equal reactivity in addition to unsaturated compounds, despite the difference in the donor-acceptor properties of the substituents at the vinyl group. In a comparison of the reactivity of radicals R⁶ and R⁷ with the reactivity of radicals CCl₃CH₂H₂(R¹), CCl₃CH₂HCH₃(R³), CCl₃CH₂HCl(R⁴), and ClCH₂CH₂Cl₂(R⁵) [1] in addition reactions, it was shown that polar and steric effects of the substituents situated in the -position to the radical site of the above-mentioned radicals, as well as the donor-acceptor properties of the substituents at the vinyl group in the unsaturated compounds, lead to appreciable changes in reactivity.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 136–141, January, 1992.     

An ESR study of the products of multiple addition of diisopropoxyphosphoryl radicals to C60

The ESR spectra of the radicals resulting from the multiple addition of diisopropoxyphosphoryl radicals to C₆₀ have been studied. The formation of six different types of radical adducts was detected. A structure for the stable product, characterized by hyperfine coupling of the unpaired electron with two phosphorus nuclei, was proposed. The unpaired electron in C₆₀P(O)(OPrⁱ)₂ is delocalized in the same way as in alkylfullerenyl radicals,i.e., mainly over the two six-membered rings adjacent to the C-CP(O)(OPrⁱ)₂ bond.Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 11, pp. 2679–2682, November, 1996.