We have performed a systematic conformational analysis focused on the evaluation of the anomeric effect (AE) in a series of pyranose derivatives containing carbon, silicon, and germanium as anomeric centers (c*) using the MP2/aug-cc-pVDZ level of theory together with natural bond orbital (NBO) electronic structure calculations. Although, both endo- and exo-anomeric effects operate within all the systems studied; the conformational preference towards the axial (α) form can be explained in terms of the incidence of the endo-anomeric effect. The magnitude calculated for the AE is considerably higher for compounds containing carbon as c*. On the other hand, the lower magnitude of the hyperconjugative delocalizations towards antibonding exocyclic anomeric orbitals in Si- and Ge-containing compounds can be justified by the availability of energetically accessible vacant d-type orbitals in these atoms. While the conformational preference in the carbon group is purely related to a higher anomeric hyperconjugation in the α conformers, steric and electrostatic factors dictate the conformational α arrangement in the Si- and Ge-containing compounds. Implicit consideration of the solvent (water) produces a notable increase in the population of the β anomers in some of the systems into study. However, the results of NBO energy partition study performed reveal that the merely observation of a change in the α/β ratio for a given system upon solvation should not be taken as an indication of a predominant role of electrostatic effects as the origin for their anomeric preference.

中文翻译：

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含有碳、硅和锗作为异头中心的吡喃糖环衍生物的异头效应：从头开始的系统研究

我们进行了系统构象分析，重点是使用 MP2/aug-cc-pVDZ 理论水平评估一系列含有碳、硅和锗作为异头中心 (c*) 的吡喃糖衍生物的异头效应 (AE)以及自然键轨道 (NBO) 电子结构计算。虽然，内和外异头效应在所有研究的系统中都起作用；对轴向（α）形式的构象偏好可以用内异头效应的发生率来解释。对于含有碳作为 c* 的化合物，AE 的计算幅度要高得多。另一方面，含Si和Ge的化合物中反键环外异头轨道的超共轭离域的较低幅度可以通过这些原子中能量可接近的空d型轨道的可用性来证明。虽然碳基团的构象偏好纯粹与 α 构象异构体中更高的异头超共轭有关，但空间和静电因素决定了含 Si 和 Ge 化合物中的构象 α 排列。对溶剂（水）的隐式考虑会导致一些系统中 β 端基异构体的数量显着增加。然而，