LAUSR

Abstract The gas phase proton affinity (PA) and basicity (GB) of a series of extended π-systems, possessing carbonyl as the most basic sites, were calculated using the DFT-B3LYP theoretical method. The backbone of the polycyclic π-electron networks contains either pyrone, pyrolidine or thiopyrane substructures, which can be in α or λ isomer forms. The PAs of designed molecules were reported in the range of 868–1089 kJ mol−1, indicating that some of the molecules have the basicity higher than 1,8-bis(dimethylamino) naphthalene. Such high basicity is a consequence of stabilization in protonated forms, due to the formation of the six-membered aromatic rings upon protonation which stabilize the positive charge. The aromaticity indices of the rings before and after protonation were calculated. The results show that aromaticity indices in the protonated form of the designed molecules is significantly higher than the neutral one.