H-bonding is the most widely studied noncovalent interaction in chemical and biological systems. Results show that the proton stretching between a donor and an acceptor affects the strength of hydrogen bond. In some cases, eight-member ring is formed due to the resonance-assisted hydrogen bonds (RAHB) mechanism. The electrostatic nature of H-bond interactions are predicted from QTAIM and NBO analysis. Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. Commonly this reaction results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond, nitrosamine has tautomer structure.