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首页> 外文期刊>RSC Advances >Thermal stabilities and conformational behaviors of isocyanurates and cyclotrimerization energies of isocyanates: a computational study
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Thermal stabilities and conformational behaviors of isocyanurates and cyclotrimerization energies of isocyanates: a computational study

机译：异氰酸酯的热稳定性和兼容性行为和异氰酸酯的旋转旋转能量：计算研究

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摘要

Isocyanurates are cyclic trimers of isocyanate molecules. They are generally known as highly thermostable compounds. However, it is interesting how the thermal stabilities of the isocyanurate molecules will be altered depending on the substituents of their three nitrogen atoms. We performed computational investigations on the thermochemical behaviors of isocyanurate molecules with various alkyl and phenyl substituents. The cyclotrimerization processes of isocyanates are highly exothermic. Our best estimate of the enthalpy change for the cyclotrimerization of methyl isocyanate into trimethyl isocyanurate was ?66.4 kcal mol ~(?1) . Additional negative cyclotrimerization enthalpy changes were observed for n -alkyl-substituted isocyanates. This trend was enhanced with an extension of n -alkyl chains. Conversely, low negative cyclotrimerization enthalpy changes were shown for secondary and tertiary alkyl-substituted isocyanates. The n -alkyl-substituted isocyanurates were shown to be stabilized due to attractive dispersion interactions between the substituents. Meanwhile, the branched alkyl-substituted isocyanurates were destabilized due to the deformation of their isocyanurate rings. For various alkyl-substituted isocyanates, the sum of the deformation energy of the isocyanurate ring and the intramolecular inter-substituent nonbonding interaction energies was found to be linearly correlated with their cyclotrimerization energies. The cyclotrimerization energy for phenyl isocyanate was shown to have significantly deviated from the linear relationship observed for the alkyl-substituted isocyanurates. This is probably attributable to a remarkable change in the orbital resonance interactions during the cyclotrimerization of phenyl isocyanate to triphenyl isocyanurate.
机译：异氰脲酸盐是异氰酸酯分子的循环三聚体。它们通常被称为高温稳定化合物。然而，有趣的是如何根据其三个氮原子的取代基改变异氰脲酸酯分子的热稳定性。我们对具有各种烷基和苯基取代基的异氰脲酸酯分子的热化学行为进行了计算研究。异氰酸酯的循环化方法是高度放热的。我们对焓变化的最佳估计，用于甲基异氰酸甲酯将甲基异氰脲酸甲酯己二酸酯α66.4kcal〜（α1）。对于N-烷基取代的异氰酸酯，观察到额外的负旋转焓焓变化。这种趋势随着N-烷基链的延伸而增强。相反，显示了仲和叔烷基取代的异氰酸酯的低负循环焓焓变化。由于取代基之间的吸引性分散相互作用，显示了N-烷基取代的异氰脲酸酯稳定。同时，由于其异氰脲酸酯环的变形，支化的烷基取代的异氰脲酸盐稳定性不稳定。对于各种烷基取代的异氰酸酯，发现异氰脲酸酯环的变形能量和分子内克分子间的非粘结性相互作用能量与它们的循环化能量线性相关。示出了苯基异氰酸酯的旋转反式化能量，从观察到的烷基取代的异氰脲酸酯的线性关系显着偏离。这可能是可归因于在苯基异氰酸酯对三苯基异氰脲酸酯的苯基旋转中的轨道共振相互作用的显着变化。

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