Theoretical Study of the Internal Rotational Barriers of Fluorine, Chlorine, Bromine, and Iodine-substituted Ethanes

Publication date: Available online 12 September 2019Source: Computational and Theoretical ChemistryAuthor(s): Sílvio Quintino de Aguiar Filho, Adão Marcos Ferreira Costa, Igor Hernandes Santos Ribeiro, Rogério Custodio, Douglas Henrique PereiraAbstractPhysical 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, C2H5l, C2H4l2, and C2H3l3. 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 Decom...

Source: Computational and Theoretical Chemistry - September 13, 2019 Category: Chemistry Source Type: research