Nuclear Magnetic Resonance Spectroscopy. Ring Inversion in 3,5,7-Cyclooctatrienone

The rate of ring inversion in 3,5,7-cyclooctatrienone was determined by the temperature dependence of the nmr spectrum of the methylene protons adjacent to the carbonyl group. Inversion does not occur by rapid reversible formation of hydroxycyclooctatetraene because deuterium exchange of the methylene protons is much too slow for the operation of such a mechanism. It is suggested that a nearly planar transition state is involved. The activation energy for ring inversion was determined to be 11.9 ± 0.5 kcal/mole