Abstract
DFT calculations were performed to analyze those interactions; B3LYP and B3PW91 methods were applied and the following basis sets were used: 6-311++G(2d, 2p), 6-311++G(3df, 3pd) and aug-cc-pVDZ. The natural bond orbital (NBO) analysis and atom in molecules (AIM) theory were applied to understand the nature of the interactions. The most stable complex NS1 with an eight-membered cyclic structure contains two O- H· ··O and N-H·· ·O hydrogen bonding interactions. From the values of r(r) at O·· ·H critical points, it can be concluded that the H-boding in eight-membered cyclic NS1 is stronger than other. The elongation of the O-H bond length is caused by the electron-density transfer to the O-H antibonding orbital.