Carbon-13 Magnetic Resonance Chemical Shifts in Alkylbiphenyls
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概要
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Carbon-13 NMR spectra were observed for the seventeen alkyl biphenyls. For the <I>meta</I>- and <I>para</I>-alkyl derivatives, the observed ring carbon-13 chemical shifts could be adequately understood in terms of the Karplus-Pople's formula by taking into account the hyperconjugative effect of the substituents. The observed chemical shifts of aliphatic carbon were in good agreement with the values of the corresponding alkylated benzenes within the limits of experimental error. For the <I>ortho</I>-derivatives, the conformation of substituents in the hindered biphenyls was particularly discussed in relation to the observed alkyl carbon-13 chemical shifts. In the cases of 2,2′-dimethylbiphenyl and 2,2′,6,6′-tetramethylbiphenyl, the chemical shifts of methyl carbons at the <I>ortho</I>-position revealed a high field shift of about 1 ppm, but that of 2,4,6-trimethylbiphenyl indicated only 0.4 ppm. The different shifts of the <I>ortho</I>-methyl carbons in the two cases suggested a spece interaction between the two methyl groups. This interaction may arise an orbital overlap between the methyl groups, which were considered to approach one another to take the <I>cis</I>-conformation.
- 公益社団法人 日本化学会の論文
著者
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Ishizu Kazuhiko
Department Of Chemistry Faculty Of Science Ehime University
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Hasegawa Hideo
JEOL (U.S.A.), Inc.
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Imanari Mamoru
JEOL, Akishima
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