Density functional theory (DFT) and ab initio (Hartree–Fock) calculations employing the 6-31G∗∗ basis set were used to determine gas-phase proton microaffinities (PAn,i) of five linear tetraamines with general formula NH2(CH2)2NH(CH2)nNH(CH2)2NH2 (where n = 2, 3, 4, 5 and 6). The corresponding proton macroaffinities () were calculated according to our recently established method with and without considering Boltzmann distribution of microspecies. The results showed that there are good correlations between the calculated proton macroaffinities, , and proton overallaffinities, log , of these tetraamines in the gas phase with corresponding protonation macroconstants, log Kn, and overall protonation constants, , in solution, respectively.
