Proton affinities and relative basicities of two 1,4,7-triazacyclononanes, Me3TACN and TP-TACN. Quantum-chemical ab initio calculations, solution measurements, and the structure of [TP-TACN·2H]2+ in the solid state

Quantum-chemical ab initio calculations have been carried out to determine the proton affinities of tripyrollidinyl- and 1,4,7-trimethyl-1,4,7-triazacyclononane. Due to an effective stabilization of the ammonium cations the proton affinities of both compounds have been found to be up to 20 kcal/mol higher than the values of non-cyclic tertiary aliphatic amines. The computational results have been compared to those from solution measurements and X-ray structure determination.