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Published March 1969 | public
Journal Article

Nuclear Magnetic Resonance Spectroscopy. Conformations and Conformational Equilibration of Some Cyclooctane Derivatives


A study of the temperature dependence of the ^(19)F nuclear magnetic resonance spectra of 1,1-difluorocyclooctane and 1,1,4,4-tetrafluorocyclooctane has shown that these substances, at low temperatures, prefer to assume the boat-chair conformation. At higher temperatures, pseudorotation within the boat-chair series of conformations becomes rapid and, at still higher temperatures, equilibrations leading to ring inversion become rapid on the nmr time scale. 1,1,2,2-Tetrafluorocyclooctane, at low temperatures, appears to prefer the twist-boat (S_4) conformation and, at higher temperatures, pseudorotation through the boat-boat conformations becomes rapid. At still higher temperatures, ring inversion becomes rapid on the nmr time scale. At low temperatures, perfluorocyclooctane seems to prefer (i) the twist-boat or (ii) the boat-boat conformation. If i, then even at - 173º, pseudorotation through the boat-boat conformation must be rapid. At room temperature, what amounts to ring inversion of perfluorocyclooctane is rapid, apparently by way of equilibration with a conformation(s) outside the boat series. Activation parameters have been obtained for several of these pseudorotation and inversion processes.

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© American Chemical Society. Received July 16, 1968. Work supported by the National Science Foundation. Presented in part at the Nineteenth National Organic Chemistry Symposium of the American Chemical Society, Tempe, Ariz., June 17, 1965. Harkness Fellow of the Commonwealth Fund of New York.

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