Abstract

The effects of the stereoelectronic interaction on the structural and conformational properties of fluoromethyl methyl ether (1) and its analogues containing Cl (2), Br (3), and I (4) atoms were investigated by means of hybrid-density functional based method (B3LYP/Def2-TZVPP) and natural bond orbital (NBO) interpretation. Consistent with the reported experimental data, the chiral gauche conformations of compounds 1–4 are more stable than their corresponding anti conformations. The results showed that the energy barriers of the racemization processes of the chiral gauche-conformations of compounds 1–4 via the plane symmetrical anti conformations are smaller than the plane symmetrical eclipsed transition structures. According to the NBO analysis, the hyperconjugative generalized anomeric effect (HCGAE) increased from compound 1 to compound 4, which explains the increase of the energy discrepancy between their corresponding chiral gauche- and plane symmetrical anti-conformations. In contrast to the trend for the HCGAE, the determined dipole moment discrepancy between the chiral gauche- and plane symmetrical anti-conformations (µ_anti–µ_gauche) reduced from compound 1 to compound 4. This fact reveals that there is no correlation between the variations of the conformational preferences in compounds 1–4 and the electrostatic effects associated with the dipole–dipole interactions. There is an excellent agreement between the racemization energy barriers and the proportion between the GAE for compounds 2–4 and compound 1 (i.e., GAE_x/GAE₁) as well as the difference between the Wiberg Bond Indexes of C₁–O₂ bonds (Δ[WBI_anti-gauche(C₁–O₂)]). The associations between the HCGAE, pairwise steric exchange energies (PSEE), WBI, dipole moments, orbital integrals, structural parameters, and conformational behaviors of compounds 1–4 have been studied.

中文翻译：

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手性薄纱的起源-卤代甲基甲醚中的构象偏好。混合密度泛函研究和自然键轨道解释

摘要

通过基于混合密度泛函的方法研究了立体电子相互作用对氟甲基甲基醚（1）及其含Cl（2），Br（3）和I（4）原子的类似物的结构和构象性质的影响（B3LYP / Def2-TZVPP）和自然键轨道（NBO）解释。与文献报道的实验数据，化合物的手性构象笨拙一致1 - 4比它们的相应的反构象更稳定。结果表明，手性的外消旋化过程的能量壁垒笨拙化合物-conformations 1 - 4通过平面对称的反构象小于平面对称的蚀变过渡结构。根据NBO分析，超共轭广义异头作用（HCGAE）从化合物1增加到化合物4，这说明它们相应的手性薄纱状和平面对称反构象之间的能量差异增加。与此相反的趋势为HCGAE，手性之间所确定的偶极矩差异笨拙-和平面对称抗-conformations（μ_抗-μ_笨拙从化合物还原的）1到化合物4。这一事实表明，没有构象偏好的变化之间化合物中的相关性1 - 4和对偶极-偶极相互作用相关联的静电效应。外消旋能垒与化合物2 – 4和化合物1的GAE比例（即GAE _x / GAE ₁）以及C ₁ –O ₂键的Wiberg键指数之间的差异之间存在着极好的协议（Δ[ WBI_防纱布（C ₁ –O₂）]）。的之间的关联HCGAE，两两空间交换能量（PSEE），WBI，偶极矩，轨道积分，结构参数，和化合物的构象行为1 - 4进行了研究。