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Theoretical study of the internal rotational barriers of fluorine, chlorine, bromine, and iodine-substituted ethanes
Computational and Theoretical Chemistry ( IF 2.8 ) Pub Date : 2019-09-12 , DOI: 10.1016/j.comptc.2019.112589
Sílvio Quintino de Aguiar Filho , Adão Marcos Ferreira Costa , Igor Hernandes Santos Ribeiro , Rogério Custodio , Douglas Henrique Pereira

Physical and chemical characteristics of flexible compounds are extremely dependent of internal rotation barriers. On the other hand, halides of organic compounds are extremely common, and the nature of their rotation barriers are still poorly understood. As a simple example, the experimental height of the internal rotational barrier decreases with the number of fluorine-substituted in ethane, C2H5F, C2H4F2, and C2H3F3. For chlorine-substituted ethane C2H5Cl, C2H4Cl2 and C2H3Cl3 the internal rotational barrier converges in an opposite manner. No experimental results are available for the bromine- and iodine-substituted compounds C2H5Br, C2H4Br2, C2H3Br3, C2H5I, C2H4I2, and C2H3I3. In light of lack of both an adequate explanation for this phenomenon and experimental results for Br and I, the present work studied these compounds using different levels of theory: MP2, MP3, MP4, QCISD(T) and CCSD(T) methods, and the G3 and G3CEP composite theories. The results showed that the G3 and G3CEP theories were the most accurate calculations for the F- and Cl-substituted compounds as a result of the additive contributions of the energy values. From Natural Bond Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Energy Decomposition Analysis (EDA) it was verified that the internal rotational barriers decrease with the addition of Fluorine atoms for fluorine-containing ethanes and can be explained by: π character in the CF bond and delocalization indexes (DI(A)) by QTAIM analysis; the interaction of the ligand and anti-ligand orbitals by NBO analysis and for the descriptors by EDA. On the other hand, the enlargement of the barriers with the addition of Cl, Br and I atoms for substituted ethanes, are dominated by the large electronic cloud of these halogens, which generates significant steric repulsion.



中文翻译:

氟,氯,溴和碘取代的乙烷内部旋转壁垒的理论研究

柔性化合物的物理和化学特性非常依赖内部旋转壁垒。另一方面,有机化合物的卤化物极为普遍,其旋转屏障的性质仍知之甚少。作为简单的例子,内部旋转屏障的实验高度随着乙烷,C 2 H 5 F,C 2 H 4 F 2和C 2 H 3 F 3中被氟取代的数目而降低。对于氯取代的乙烷,C 2 H 5 Cl,C 2 H 4 Cl 2和C 2 H33以相反的方式内部旋转屏障收敛。对于溴和碘取代的化合物C 2 H 5 Br,C 2 H 4 Br 2,C 2 H 3 Br 3,C 2 H 5 I,C 2 H 4 I 2和C 2没有可用的实验结果。^ h 33。鉴于对这种现象以及Br和I的实验结果都缺乏足够的解释,本研究使用不同水平的理论对这些化合物进行了研究:MP2,MP3,MP4,QCISD(T)和CCSD(T)方法,以及G3和G3CEP综合理论。结果表明,由于能值的加和作用,G3和G3CEP理论是F和Cl取代化合物的最准确计算。从自然键轨道(NBO),分子原子量子论(QTAIM)和能量分解分析(EDA)中,可以证明,随着含氟乙烷的添加氟原子,内部旋转势垒会降低,可以通过以下方式解释: C F键和离域指数(DI(A))通过QTAIM分析;通过NBO分析确定配体和抗配体轨道之间的相互作用,并通过EDA确定描述符。另一方面,为取代的乙烷添加Cl,Br和I原子而增加的势垒主要由这些卤素的大量电子云所控制,这会产生明显的空间排斥力。

更新日期:2019-09-12
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