Nuclear magnetic resonance study of exchanging systems. XI. 13C NMR spectra of 9-ethyltriptycene derivatives and the restricted rotation of the ethyl group.

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概要

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• 9-Ethyl-1,4-dimethoxytriptycene, 1,5-dichloro-9-ethyltriptycene, and 9-ethyl-1,4-dimethyltriptycene were prepared. The <SUP>13</SUP>C NMR spectra of these compounds were measured at low temperatures in order to obtain information about the restricted rotation of the ethyl group. It was found that the former two compounds have the <I>meso</I> isomer as well as the <I>dl</I> isomer. Different chemical shifts of the methylene carbons in the ethyl group, C(2) and C(3) of the benzene A ring, and some quaternary carbons in the two isomers of 9-ethyl-1,4-dimethoxytriptycene indicate that the 120°C rotation around C<SUB>sp<SUB>3</SUB></SUB>–C<SUB>sp<SUB>3</SUB></SUB> single bond in the ethyl group deforms the benzene or bicyclo[2.2.2]octatriene skeleton. The complete line-shape analyses of the temperature-dependent <SUP>13</SUP>C NMR spectra of this compound were performed, and the thermodynamic static parameters and activation parameters of the ethyl rotation were determined. The correlation between the rotational barriers of the alkyl groups and their bulkiness was briefly discussed.

• 公益社団法人 日本化学会の論文

著者

• NAKANISHI Hiroshi

  National Chemical Laboratory for Industry

• YAMAMOTO Osamu

  National Chemical Laboratory for Industry

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