Investigation of Hydrophobic Effect on the Hydrogen-Bond Formation of 1,1,3,3-Tetramethylurea by Raman Methods

The binary systems of 1,1,3,3-tetramethylurea (TMU) with water, TMU with methanol, TMU with ethanol and N,N-dimetliylformamide(DMF) with water were measured by Raman method. With the analysis of the frequency changes of stretching vibration of carboxyl with concentration the authors found that the frequency shift underwent two processes: first, the frequency of stretching vibration of carboxyl down shifts with the increase in hydrogen-bond acceptor concentration; secondly, when the concentration of binary system surpasses a critical value, the wave number remains almost constant, and only the relative intensity changes. Through this critical volume ratio, the authors found that the large self-associated water molecule was involved in the TMU aqueous binary system; while the small self-associated molecule or dimer formation was present in other binary systems.