Hydrogen bonding of formamide, urea, urea monoxide and their thio-analogs with water and homodimers

Abstract

Ab initio and DFT methods have been employed to study the hydrogen bonding ability of formamide, urea, urea monoxide, thioformamide, thiourea and thiourea monoxide with one water molecule and the homodimers of the selected molecules. The stabilization energies associated with themonohydrated adducts and homodimers’ formation were evaluated at B3LYP/6-311++G** and MP2/6-311++G** levels. The energies were corrected for zero-point vibrational energies and basis set superposition error using counterpoise method. Atoms in molecules study has been carried out in order to characterize the hydrogen bonds through the changes in electron density and laplacian of electron density. A natural energy decomposition and natural bond orbital analysis was performed to understand the nature of hydrogen bonding. Sixteen hydrogen bonded adducts of formamide, urea and urea monoxide with one water molecule and their homodimers have been optimized at B3LYP/6-311++G** and MP2/6-311++G** levels. Monohydrated Adducts and homodimers formation with the corresponding thio-analogs were also studied for comparative purpose. Atoms in molecules study has been carried out in order to characterize the hydrogen bonds. A natural energy decomposition and natural bond orbital analysis were performed to understand the nature of hydrogen bonding.