Formamide And Its Derivatives On Hydrogen Bonding Clusters Ab Initio Calculations

Hydrogen bonds play a central role in the function and structure of all biological molecules. So it is important to study the hydrogen bonded clusters in order to understand the functions.There are peptide bonds in the molecules of formamide, N-methyl formamide or N, N-methyl formamide. A proton transfer can occur between different moieties of the same molecule. And the proton transfer is one of the most important and the most essential chemical reactions. So study those molecules is of special biological significance.The intramolecular hydrogen transfer of both formamide and its derivatives in the presence of water, ammonia, methanol and hydrogen fluoride are studied by hybrid functional method (B3LYP) in conjunction with 6-311++G** basis set. The hydrogen transfer process of formamide and its derivatives were simply described in the presence of water, ammonia, methanol and hydrogen fluoride. Based on the present calculations the isomerization energy barriers between formamide and formamidic acid are reduced when it was catalyzed with a solvent molecule (water, ammonia, methanol or hydrogen fluoride). The calculationanl resultes show that the catalytic effect of the solvent molecules is difference from each others for formamide, N-methyl formamide and N, N-methyl formamide. The catalytic effect of hydrogen fluoride is the most effective, and the effect of ammonia is the most weak among the four molecules.The NMF-water clusters are studied by ab inito calculations at MP2/6-31+G** and MP2/6-311++G** levels. For N-methyl formamide, cis-form has lower energy than trans-form. In NMFH+, the proton prefers to link with the O atom of N-methyl formamide. The equilibrium geometries and the dissociation channels and dissociation energies of both neutral and ionic NMF-H2O clusters are presented. The results show that although the energy of trans-NMF is higher than cis-NMF, trans-form exits more stable because it can form a double hydrogen bond with water. After the ionization of the NMF-H2O cluster, both the cis- and the trans-form will produce protonated products.