Hydration Structure around the Carbonyl Group of an Urea Molecule in Concentrated Aqueous Solutions Studied by Neutron Diffraction with 12C/13C Isotopic Substitution

Abstract

Abstract Neutron diffraction measurements were carried out at 25 °C on aqueous 15 mol % urea heavy water solutions, [(ND2)2*C=O]0.15(D2O)0.85, in which the 12C/13C isotopic composition of the carbonyl-carbon atom was changed. The hydration structure around the carbonyl-carbon atom was derived from the least-squares fitting analysis of the observed first-order difference function, ΔC(Q). From the analysis, 4.3(3) water molecules are hydrogen-bonded to the carbonyl-oxygen atom with the intermolecular C···DW1 (DW1: water deuterium atom) distance of 2.46(3) Å. The average angle, ∠C···DW1–OW (OW: water oxygen atom), was determined to be 124(5)°.