Isamu Nitta

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.

Crystal Structure of 2-Amino Azulene

A systematization was proposed for the determination of the crystal structure when the crystal consists of the molecules with known shape. The main feature of this method is to separate the refinements by the least squares at an early stage into (1) successive improvements of the position and orientation of the molecule and (2) correction of the molecular shape fixing the molecular position and orientation. The result of the application of this method to the crystal of 2-amino azulene ( a =11.62, b =10.76, c =6.32 A, Z =4, space group P b n 2 1 ) was given.

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.

The X-ray analyses of acutumine and its acetate; a trial of a short cut in the structure elucidation

The crystal and moleular structures of acutumine, a novel type of alkaloid containing chlorine, and of its acetate, have been solved by X-ray analysis using a three-dimensional Patterson superposition method and repeated application of least squares and three-dimensional Fourier methods. The result agreed with the chemical evidence obtained by concurrent degradative studies. The structure of acutumine is closely related to that of hasubanonine which was isolated from a species of the same plant family, but has a spiran-type juncture of the five-membered rings A and B, with a chlorine atom attached to the latter.The usefulness of applying the least-squares method at an unusually early stage for distinguishing real atoms from the spurious peaks appearing in the maps of minimum functions or of Fourier synthesis was clearly demonstrated. In particular, observation of the behaviour of temperature factors through several cycles of least-squares with fixed atomic co-ordinates was found to provide a rapid method.

Infrared Absorption Spectra of Polyvinyl Alcohol Films Swollen in Water

Infrared absorption spectra were measured of three kinds of polyvinyl alcohol films, swollen in liquid water at 25°C for two days. These three kinds of specimens were prepared from the same PVA powder specimen and subjected to different heat-treatments;no heat-treatment (I), 100°C, 30min.(II) and 160°C, 15min.(III).It was observed in the present study that the crystallization-sensitive band (1146cm-1) is hardly found in the spectra of the swollen samples (I) and (II) but appears progressively as the samples are being dried. On thee other hand, in the case of sample III this band appears not to be effected strongly by swelling.This observation is consistent with our previous results about the X-ray-measurements that the crystalline regions of the swollen PVA films, except a film subjected to strong heat-treatment, are penetrated by water molecules at room temperature.