H-1 NMR studies (400 MHz) on isopropoxycyclooctatetraene (C8H7-O-C3H7) and its ring-d(7) analogue (C8D7-O-C3H7) show that there is an inverse isotope effect on the rate of ring inversion of k(H)/k(D) = 0.68-0.57 in the temperature range from -10 to -50 degrees C. These experiments confirm the validity of previously published DFT calculations on cyclooctatetraene/cyclooctatetraene-d(8), which predict an inverse isotope effect of about this size on the rate of ring inversion in this temperature range. The large inverse isotope effect upon ring inversion explains why the similarly large normal equilibrium isotope effect, found in the reduction of benzene to its corresponding anion radical, is not observed in the analogous reduction of cyclooctatetraene.