Shun-Ichi Ohnishi

ESR Study of Free Radicals Produced by Irradiation in Benzene and Its Derivatives

Benzene and some of its mono‐ and di‐substituted derivatives including toluene, chlorobenzene, benzoic acid, phenylcyclohexane, polystyrene, and xylenes were irradiated in their solid state at —196°C. After the irradiation their ESR spectra were measured at that temperature and also up to their melting points. The spectrum of benzene consisted of two components. One was a main triplet (splitting 47.5 G) with a quartet substructure (splitting 10.4 G), each quartet showing further fine (probably triplet) splitting of ∼2.5 G, and it was assigned to cyclohexadienyl radical C6H7·. When the temperature was raised this spectrum showed a marked narrowing from about —173°C where the C6 reorientation of the benzene molecule sets in. At the same time the radical began to diminish, and decayed out at —32°C, which is far below the melting point. The other component of the spectrum was a singlet of 25‐G width at the maximum slope, and was assigned to phenyl radical C6H5·. This component decayed out at 0°C. The spectra of the benzene derivatives were triplet, quite similar to that of benzene, and were interpreted to be due to the radicals produced as a result of hydrogen addition to the benzene ring. The GR values determined at —196°C for benzene, cyclohexane, their 1:1 mixture, and phenylcyclohexane were 0.14, 5.04, 2.4 and 0.66, respectively. It is concluded that in the case of phenylcyclohexane some energy‐transfer process may occur from the cyclohexyl ring to the phenyl ring.

Electron spin resonance studies of irradiated polymers I. Factors affecting the electron spin resonance spectra of irradiated polymers

Abstract Electron spin resonance spectra of the trapped intermediates at room temperatures in irradiated polymers have been measured for fourteen kinds of polymers in order to obtain information on the mechanism of radiation chemical processes. The present report concerns the identification of radical species from the spectral shape. Radicals trapped in irradiated polyethylene, polypropylene and poly(vinyl alcohol) have been identified tentatively. The following factors were found to affect and complicate the observed spectral shape: (1) coexistence of several kinds of radicals; (2) effect of state of aggregation of polymer on the spectra; (3) effect of irradiation dose and dose rate on the spectra.

Photoinduced Change of Organic Free Radicals as Studied by ESR. I. Conversion of Allyl‐Type to Alkyl‐Type Radicals in Irradiated Polyethylene

The allyl‐type radical –CH2–ĊH–CH=CH–CH2– in irradiated polyethylene was converted into the alkyl‐type radical –CH2–ĊH–CH2– upon uv illumination (λ 2537 A). During the conversion total concentration of the radicals remained constant. The production curve of the alkyl‐type radical reached a saturation at 43% conversion. Initial rate of production of the alkyl‐type radical was found proportional to the light intensity, while the saturation concentration was the same for illuminations of different intensities. The initial rate was independent of the illumination temperature and of presence of added hydrogen gas. A reaction mechanism which involves an intramolecular hydrogen atom shift was put forward: –CH2–CH2–CH–CH=CH–⇌ lim k2k1–CH2–ĊH–CH2–CH=CH–. The corresponding kinetic equation was solved and the rate constants k1 and k2 as well as the quantum yield were calculated from experimental results. It was found that this mechanism would explain all the features of the reaction satisfactorily. In addition to c...

ESR Study of Free Radicals Produced in Irradiated Cyclopentadiene and Cyclohexene: The Cyclopentadienyl and Cyclohexenyl Radicals

The ESR spectra of irradiated cyclopentadiene and cyclohexene were measured at various temperatures. The spectra showed motional narrowing on raising temperature and the free radicals were identified from analysis of the narrowed spectra. Cyclopentadiene showed a well‐resolved sextet spectrum of 5.6‐G splitting, which was assigned to the cyclopentadienyl radical. Cyclohexene gave a spectrum consisting at least of 26 lines, which can be reasonably attributed to the cyclohexenyl radical by assuming appropriate hyperfine constants.

Conformation and Reaction of Stereoisomeric Radicals Trapped in Irradiated cis‐ and trans‐Cyclohexane−1,2‐diol

ESR measurements were carried out on the samples of electron‐irradiated cyclohexanediols. In the case of 1,2‐diols, the results are consistent with an interpretation of trapping of two conformationally isomeric radicals, cis‐ and trans‐cyclohexane−1,2‐diol−1, at −196°C and their intramolecular conversion to cyclohexanone−2 or 2‐hydroxycyclohexanone−6 radicals upon warming to room temperature.

ESR STUDY OF FREE RADICALS PRODUCED IN SOME ORGANO-SULFUR COMPOUNDS BY IRRADIATION AT -196 DEG C

低温(-196℃)で電子線照射した無定形, または多結晶状態の種々の有機イオウ化合物(-SH,-S-S-または-C-S-C-含むもの)のESRが-196℃ から室温までの温度範囲で測定され,次の事実が明らかにされた。アルキルメルカプタンにおいては,アルキル基の炭素数が3の場合には主としてR-S・形のラジカルが生じるが,炭素数が多い場合には,アルキル形ラジカル-CH2-CH-CH2-が多く生じてくる。シスチンではイオウに不対電子が局在したラジカルのみしか生じないのに, ホモシスチンでは, イオウのラジカルも生じるが, 炭素のラジカルが逆に優勢となる。ペンゼン環とS - S 結合を含むジフェニルジサルファイドとジベンジルジサルファイドではイオウのラジカルのみが生じた。すなわちいずれの場合にもR-S・が生じる他,ジフェニルジサルファイドでは,さらに別種のラジカルが生じ,これは,イオン化ラジカル〓に同定される。C-S-Cの結合を分子中に含むジ-n-ブチルサルファイドとS-ベンジル-L-システインにおいては, 低温では他のラジカルも混在するが, 昇温すると-CH-S-CH2-型のラジカルのみが安定になる