The foe energies of activation for bond shift in the carbon group substituted cyclooctatetraenes (COT-M(CH3)(3)) in THF-d(8) at 298 K have been determined to be 16.4, 16.2, 16.2, and 18.1 kcal/mol for M = Si, Ge, Sn, and C, respectively, and 15.6 kcal/mol for CH3-COT. These data permit an interpretation of the previously reported opposite orders for the ease of the first and second electrochemical reductions in the Si, Ge, and Sn compounds. It is postulated that the order of the first reduction potential is controlled by a decrease in overlap between the substituent and the ring pi orbitals in the order Si > Ge > Sn, whereas the second reduction potential is controlled by the energy gap between the symmetric pi HOMO of the COT radical anion and an interacting substituent sigma* orbital of pi symmetry (epsilon(sigma*pi) - epsilon(pi)), which increases in the order Sn < Ge < Si. HF/3-21G molecular orbital calculations indicate that the high barrier for t-Bu-COT primarily reflects steric effects in the transition state.