Wydział Chemii

Monika H. Obrzud

Maria Rospenk

Aleksander Koll

2014

Physical Chemistry Chemical Physics

16

3209-3219

10.1039/c3cp53582g

Naukowa

Angielski

Artykuł

The mechanisms of self-aggregation ofN-alkyl andN,N0-dialkyl derivatives of urea and thiourea in weaklypolar solvents (chloroform and 1,2-dichloroethane) were examined. The C–HOorC–HS hydrogenbonds formed with these two acidic solvents compete with the N–HOorN–HShydrogenbondsformed between solute molecules, influencing the self-aggregation of urea derivatives in a particularsolvent. The peculiarities of the solvent interactions were discussed and the stronger interaction ofchloroform was noted. Aggregation of theN-alkyl derivatives was followed using IR spectroscopy, with twogradual aggregation constants (K1andK2) determined. The average molecular weight and dipole momentswere shown to depend on the concentration, and the form of aggregation was analyzed through the studyof the dipole moments. All of the urea derivatives demonstrated an increase in dipole moment withincreased concentration, resulting in stronger NH2O hydrogen bond interactions and leading to linear-type aggregation. Contrastingly, the dipole moments of the mono-N-alkyl-substituted thioureas decreasedwith concentration. Density-functional theory calculation of these processes showed that reliable resultscould only be obtained if solvent interactions were considered, with a specific combination of local andbulk effects. It was also shown that going fromN,N0-disubstituted toN-monoalkyl derivatives the ability toaggregate increases, which is related to a diminished steric hindrance to hydrogen bonding. Finally, it wasdemonstrated that the mechanisms of self-aggregation depend on the acid–base properties of the solute,hydrogen bonding to the solvent molecules, and steric interactions of the aliphatic chains.

http://dx.doi.org/10.1039/c3cp53582g

https://www.rsc.org/