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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
Author(s) -
Anet Frank A. L.,
Easton N. Roy,
Yavari Issa
Publication year - 1979
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270120510
Subject(s) - chemistry , 1,5 cyclooctadiene , cyclooctadiene , spectral line , nmr spectra database , stereochemistry , catalysis , organic chemistry , physics , astronomy
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.