3, 3, 6, 9, 9-Pentamethyl-2, 10-diazabicyclo [4.4. 0] dec-1-ene has been synthesized and its proton transfer reactions, together with those of the bases 2, 2, 6, 6-tetramethylpiperidine and 1, 2, 2, 6, 6-pentamethylpiperidine, have been studied with the carbon acids 4- nitrophenylphenylcyanomethane and 2-methyl-4-nitrophenylphenylcyanomethane. Equilibrium constants, rate constants, primary deuterium isotope effects, and activation ...