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首页> 美国卫生研究院文献>Molecules >Diradicalar Character and Ring Stability of Mesoionic Heterocyclic Oxazoles and Thiazoles by Ab Initio Mono and Multi-Reference Methods
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Diradicalar Character and Ring Stability of Mesoionic Heterocyclic Oxazoles and Thiazoles by Ab Initio Mono and Multi-Reference Methods

机译：AB Initio Mono和多参考方法的Diradical杂环恶唑和噻唑的Diradicalar字符和环稳定性

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摘要

Mesoionics are neutral compounds that cannot be represented by a fully covalent or purely ionic structure. Among the possible mesomeric structures of these compounds are the diradical electronic configurations. Theoretical and experimental studies indicate that some mesoionic rings are unstable, which may be related to a significant diradical character, that until then is not quantified. In this work, we investigated the diradical character of four heterocycles: 1,3-oxazol-5-one, 1,3-oxazol-5-thione, 1,3-thiazole-5-one, and 1,3-thiazole-5-thione. The oxazoles are known to be significatively less stable than thiazoles. DFT and ab initio single (B3LYP, MP2, CCSD, and QCISD) and ab initio multi-reference (MR-CISD) methods with three basis sets (6-311+G(d), aug-cc-pVDZ, and aug-cc-pVTZ) were employed to assess the diradical character of the investigated systems, in gas phase and DMSO solvent, from three criteria: (i) HOMO-LUMO energy gap, (ii) determination of energy difference between singlet and triplet wave functions, and (iii) quantification of the most significant diradical character (y0, determined in the unrestricted formalism). All of the results showed that the diradical character of the investigated systems is very small. However, the calculated electronic structures made it possible to identify the possible origin of the oxazoles instability, which can help the design of mesoionic systems with the desired properties.
机译：中性学是中性化合物，其不能通过完全共价或纯属离子结构表示。在这些化合物的可能的间聚结构中，是Diradical电子配置。理论和实验研究表明，一些中间环环是不稳定的，这可能与显着的Diradical特征有关，直到那么未量化。在这项工作中，我们研究了四种杂环的Diradical特征：1,3- oxazol-5-on，1,3-恶唑-5-thione，1,3-噻唑-5-一，1,3-噻唑 - 5岁。已知恶唑比噻唑更稳定。 DFT和AB Initio单（B3Lyp，MP2，CCSD和QCISD）和AB Initio多参考（MR-CISD）方法，具有三个基础集（6-311 + G（D），Aug-CC-PVDZ和AUG-使用CC-PVTZ）从三个标准中评估研究系统，气相和DMSO溶剂中的Diradical特征：（i）Homo-Lumo能量隙，（ii）单态和三联波函数之间的能量差异， （iii）量化最重要的Diradical字符（Y0，在不受限制的形式主义中确定）。所有结果表明，研究系统的Diradical特征非常小。然而，计算出的电子结构使得可以识别恶唑不稳定性的可能起源，这可以帮助设计具有所需特性的中间因子。

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