Research of Plastic-like crystalline phases and thermal properties of urea and thiourea derivatives with long chain alkyl groups

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For such compounds as n-butylurea, n-octylurea, symmetric N, N-dibutylurea and dodecylthiourea, plastic-like crystalline phases were found by thermal analyses (DSC). In these cases, the entropy jump of the transition from normal to plastic-like phases amounts to 1/3 1/2 of that of fusion. Single crystal X-ray study elucidated the disorder of alkyl groups in the plastic-like phases and their dynamic nature were studied by solid state NMR methods.Phase transitions were often detected for n-alkylureas. Crystal structure determinations at various temperatures revealed that the mechanism of these transitions was one or two-directional mutual slip of two-dimensional supramolecules constructed by N-H O hydrogen bonds. N-methyl, N-alkylureas with long chain alkyl groups exhibited a common phase transition in the vicinity of melting point. The mechanism of this transition would be similar to that of the n-alkylureas.N-methyl, N-alkylthioureas with long chain alkyl groups exhibited no phase tran … More sitions in contrast to the above cases. This observation could be ascribed to the depression of the thermal motions of the alkyl groups due to a common unique interdigitation of the groups in the crystals.Three-dimensional supramolecular assemblies with distinctive interlocking network via hydrogen bonds were seen in the crystals of 1,5-diureidopentane and 1,4-diureidobutane. DSC experiments on the compounds detected no phase transitions, but established prominent tendency of glass transitions. The crystal structure mentioned above was considered to prevent the phase transitions in the crystalline phase, but to facilitate the formation of considerably stable glassy states.Electric conduction due to proton jump appeared to be possible in butylurea and dodecylthiourea.Characteristics of some physical properties of such compounds as butylurea, octylurea and triptycenequinone could be controlled through modulations of local intermolecular interactions caused by formation of mixed crystal system.Crystal structures and thermal properties were investigated for a lot of urea and thiourea derivatives. Less