Based on Table 11, for n-2AOE13PDA and 2-MPMDA amines, the difference in energies were all positive. It means that the electronic energies of the primary protonated amines were lower than the alternative positions which were at the nitrogen closer to the functional groups. For n-2AOE13PDA and DMAPAPA amines, the difference in energies were all negative. Therefore, the electronic energy of the secondary protonated of the amines was lower than at the primary position. Similarly, for DMAPAPA and DAOMDPA amines, the different energies were positive; therefore, for the tertiary protonated structures, the electronic energies were higher than the primary positions. As a result, the secondary amino groups were probably responsible for the first pKa of n-2AOE13PDA and DMAPAPA amines while the primary amino which were away from functional groups were responsible for the first pKa of 2-MPMDA and DAOMDPA amines. As mentioned in the literature,19 the secondary amino group was protonated before the primary amino group which was in turn protonated before the tertiary amino group. The computational study was in good agreement with the literature.19