Theoretical Analysis of Stereoelectronic Effects in the 2,4,6-Trihalo-1,3,5-trioxane and 2,4,6-Trihalo-1,3,5-trithiane C
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TRUCTURE OF MATTER AND QUANTUM CHEMISTRY
Theoretical Analysis of Stereoelectronic Effects in the 2,4,6-Trihalo-1,3,5-trioxane and 2,4,6-Trihalo-1,3,5-trithiane Conformers Karim Hajhoseinzadeha, Reza Ghiasib,*, and Azam Marjania a Department
b
of Chemistry, Faculty of Science, Arak Branch, Islamic Azad University, Arak, Iran Department of Chemistry, Faculty of Science, East Tehran Branch, Islamic Azad University, Tehran, Iran * e-mail: [email protected] Received October 7, 2019; revised October 25, 2019; accepted November 12, 2019
Abstract—This research aimed at exploring the conformers stabilities of 2,4,6-trihalo-1,3,5-trioxane and 2,4,6-trihalo-1,3,5-trithiane molecules at the LC-wPBE/6-311+G(d, p) theory level. To this goal, estimations of the total energies and frontier orbitals energies of the axial and equatorial conformations were first done for the afore-mentioned molecules. C–E (E = O, S), C–X (X = F, Cl), and C–H bonds lengths were calculated and these variations were explained with negative hyperconjugative anomeric effects. In addition, QTAIM analysis was used to illustrate the character of these bonds. The partitioning of the total electronic energy E(tot) into Lewis EL and non-Lewis ENL parts was performed using the concept of natural bond orbital (NBO) analysis. Then, the natural Coulomb electrostatic (NCE) potential energies, total energies into Lewis components, and total steric energies were estimated. Proton chemical shift and C–H spin–spin coupling values (J(C–H)) of the studied molecules were calculated. Keywords: 2,4,6-trihalo-1,3,5-trioxane, negative hyperconjugative effect, conformers, natural bond orbital analysis, quantum theory of atoms in molecules (QTAIM), Ramsey approximation DOI: 10.1134/S003602442010012X
INTRODUCTION Ring systems with oxygen-, sulfur-, and seleniumcontaining molecules like 1,3,5-trioxane (TO), 1,3,5trithiane (TS) and 1,3,5-triselenane (TSe) have tremendous applications. TO is not only an automotive fuel additive but also a convenient model in atmospheric chemistry [1], extrapolation of new far infrared (FIR) laser transitions [2] besides its industrial [3] and biological [4] applications. Alternatively, TS plays an important role in the electrochemical extraction of heavy metal ions [5]. Furthermore, TS crown thioethers and TSe transition metal complexes play an essential role in the structures of molecules of biological significance [6, 7], they also acts as active centers in many redox reactions in life processes [8]. 1,3,5Dithiazinane compounds are widely used as food additives [1–3] and as adsorbents for noble metals [9]. They also exhibit fungicidal activity [10]. Theoretical calculations on 1,3,5-trifluorocyclohexane, 2,4,6-trifluoro-1,3,5-trioxane, and 2,4,6-trifluoro-1,3,5-trithiane verify hyperconjugative interactions [11, 12]. Besides the steric and electrostatic interactions, the structure, the conformational behavior, and the reactivity of organic molecules are affected stereoelectronicaly [13–18]. When a high-
energy occupied orbital is transf
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