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Carbon-13 nuclear magnetic resonance spectra and conformations of cis,cis-1,5-cyclooctadiene monoepoxide and cis, syn,cis-1,5-cyclooctadiene diepoxide

✍ Scribed by Frank A. L. Anet; N. Roy Easton Jr; Issa Yavari

Publisher
John Wiley and Sons
Year
1979
Tongue
English
Weight
313 KB
Volume
12
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The natural‐abundance ^13^C NMR spectra of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis,syn,cis‐1,5‐cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free‐energy barrier (ΔG^≠^) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol^−1^ from a line‐shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis‐1,5‐cyclooctadiene diepoxide exists in solution in chair (major) and in twist‐boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist‐boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.

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