The Intramolecular Dynamic Behavior of Tetraaryl Allyl Radicals
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概要
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The electron spin resonance (ESR) and the electron nuclear double resonance (ENDOR) spectra of tetraaryl allyl radicals have been observed. A comparison of the ENDOR spectra of α,α,γ,γ-tetraphenyl allyl, α,α-diphenyl-γ,γ-dianisyl allyl, and α,α,γ,γ-tetraanisyl allyl revealed that the four aryl groups are not equivalent, but are apparently to be classified into two types with different conformations in their molecular frameworks. The molecular orbital calculations on the basis of this model have shown a fairly good agreement with the observed spectra. The temperature dependence of the ENDOR spectra at −60∼−110 °C were analyzed, assuming mutually different twisting angles for the allyl skeleton. The activation energy of the torsional vibration of the allyl skeleton is estimated to be about 2.5 kcal/mol. The ESR spectra of α,α,γ,γ-tetraphenyl allyl and α,α-diphenyl-γ,γ-diphenylene allyl change drastically with the temperature at around +115°C and show a marked line-width alternation effect. It is concluded from the results that the torsional vibration becomes vigorous with an increase in the temperature and that the allyl skeleton begins to rotate internally at high temperatures. The activation energy of the internal rotation of the allyl skeleton has been estimated to be about 15∼20 kcal/mol. The temperature-dependent hyperfine splitting of the methine proton has also been explained by assuming a model of the internal rotation of the allyl skeleton.
- 公益社団法人 日本化学会の論文
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関連論文
- The Intramolecular Dynamic Behavior of Tetraaryl Allyl Radicals
- Studies of the Equilibria between Tetraarylallyl-type Radicals and Their Dimers
- Abnormal Hyperfine Splitting in the ESR Spectra of α,α,γ,γ-Tetraphenylallyl-type Organic Stable Free Radicals