5 | PREDICTING THE ORDER OF PROTONATION
As observed by considering the molecular structures of the compounds, two of the amines are diamines while the three of them are triamines. The structure of Bis[2-(n,n-dimethylamino)ethyl]ether is symmetrical while the other structures were not symmetrical with the presence of primary, secondary and tertiary amino groups. Therefore, it is important to study the order of protonation to better understand the reaction mechanism of the amines. In this study, the amine structures were optimized by commercial computational chemistry software [Gaussian (09 Revision B.01 SMP)] with different models and basis sets. These molecular structures were built using GaussView version 5.0.9. Water was used as a solvent with a polarizable continuum model (PCM). After structural optimization, the energy (E) of different protonated amine scenarios could be used for predicting the protonation locations. Equation 9 was used to calculate the difference in energy levels. The main chain of the organic compounds is the longest chain with additional groups attached to the chain, and are called functional groups. In the equation, EPrimary Protonated* is that of the amino group which is closer to the functional group. In the case of n-2AOE13PDA, the primary* group is the one close to the secondary amino group because its structure is straight. Table 11 shows the different energy levels for the scenarios.
ΔE(kJ·mol-1) = ESecondary/Tertiary/Primary Protonated* - EPrimary Protonated (9)
Table 11 Differences in energies between the different protonated positions