Radical pair formation in dihalogenated benzene derivatives at 77K

✍ Scribed by Tomochika Matsuyama; Hitoshi Yamaoka

• Publisher: Elsevier Science
• Year: 1979
• Tongue: English
• Weight: 267 KB
• Volume: 60
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(79)80614-4

✦ Synopsis

Radical pair formation in dihalogenated benzene derivatives irradiated at 77 K has been revealed by the EPR detection of AM= 2 transitions. In some specimens, the hydrogen atom signal has been observed, suggesting the presence of the phenyl radical Radical pairs which are theoretically characterized by trip!et ERR [14] have been investigated by many authors in a wide variety of organic compounds, because selectie formation of radical pairs is anticipated to play an important role in elucidating the initial process of radiation effects and the mechanism of enzymatic activities [S] _ Concerning aromatic compounds, our recent papers [6-S] have first dealt with the radical pair formation which has been found by detection of the weak signal for AM= 2 transition and the fine structure due to AM= 1 transition_ In these reports it has been considered that the aromatic radical pairs are composed of the phenyl-type and cyclohexadienyl-type radicals.

In this study we have further dealt w&h radical pair formation mainly in dihalogenated benzenes. The specimens examined in polycrystalline system were commercially purest grade and are listed in table 1 _ AlI specimens were irradiated by 6oCo 7 rays up to a dose of about 6 X IO* r-ads. Further details of the experimentd procedures have been described in our recent papers [S-8] _

Typical spectra recorded at 77 K immediately after the irradiation are shown in figs. 1 and 2. Curve (a) of each specimen is the signal observed in the region of g = 2_ The EPR line profie of each curve (a) is a main triplet with a hyperfme coupling constant of about 45 G and is essentially similar to that of the benzene and monohalogenated benzenes previously reported [6,7] _ This fact implies that one of the prominent products in each specimen is the cyciohexadienyl-type radical [7,9]. CUIW (a') in figs. 1C and 2C is an enlarged tail