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

对于正丁脲、正辛脲、对称N、N-二丁脲和十二烷基硫脲等化合物，通过热分析（DSC）发现了类塑料晶相。在这些情况下，从正常相到类塑相转变的熵跃相当于聚变的1/3 /2。单晶x射线研究阐明了类塑料相中烷基的无序性，并用固体核磁共振方法研究了它们的动力学性质。正烷基脲类化合物经常检测到相变。在不同温度下的晶体结构测定表明，这些转变的机制是由N-H - O氢键构成的二维超分子的单向或双向相互滑移。具有长链烷基的n -甲基、n -烷基脲在熔点附近表现出共同的相变。这种转变的机理与正烷基脲类似。具有长链烷基的n -甲基、n -烷基硫脲与上述情况相比，没有发生相转移。这一观察结果可归因于由于晶体中基团的共同独特的互指现象而使烷基的热运动减弱。在1,5-二脲基戊烷和1,4-二脲基丁烷晶体中观察到具有独特的氢键联锁网络的三维超分子组合。DSC实验检测到化合物没有发生相变，但有明显的玻璃化转变趋势。上面提到的晶体结构被认为是为了防止晶相中的相变，而是为了促进相当稳定的玻璃态的形成。在丁脲和十二烷基硫脲中，由于质子跃迁可能发生电传导。丁脲、辛脲和三苯甲马酮等化合物的某些物理性质可以通过调节混合晶体体系形成引起的局部分子间相互作用来控制。研究了多种脲类和硫脲类衍生物的晶体结构和热性能。少

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