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

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 the monohydrated 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.