M06-2X/6-31G(d)-optimized transition-state structures for the cycloadditions of 1,3- and 3,3-dimethylcyclopropene [Cp(1,3) and Cp(3,3)] with diphenyl-substituted nitrile imine (NI) and tetrazine (Tz). M06-2X/6-311+G(d,p)//6-31G(d)-computed energies and relative rate constants (distances in Å, energies in kcal/mol, krel based on Gwater at 298 K) are also shown.