Hyperconjugative interactions are the main responsible for the anomeric effect: a direct relationship between the hyperconjugative anomeric effect, global hardness and zero-point energy
Hyperconjugative interactions are the main responsible for the anomeric effect: a direct relationship between the hyperconjugative anomeric effect, global hardness and zero-point energy
复制标题
超共轭相互作用是异头效应的主要原因：超共轭异头效应、整体硬度和零点能量之间存在直接关系
作者：
D. Nori;Seiedeh Negar Mousavi;Rose Tale;H. Yahyaei
利用常规泛函和范围修正泛函以及自然键轨道（NBO）解释，研究了2-氟四氢吡喃、-硫吡喃、-硒吡喃（1-3）及其氯-(4-6)和溴类似物（7-9）的整体硬度（η）、超共轭异位效应、泡利交换型斥力、偶极-偶极相互作用相关的静电模型和结构参数之间的关系。通过删除HC-exo-AE和hc - endoo - ae，化合物1-9的赤道构象比其相应的轴向构象更加稳定，说明化合物1-9的头型关系具有超共轭的头型效应，而与偶极-偶极相互作用相关的静电模型对化合物头型关系的变化不起决定性作用。化合物1-3的异构关系不具有泡利交换型排斥源，但对化合物4-6和7-9的构象偏好有显著影响。采用典型分子轨道解释方法研究了HOMOs、LUMOs中天然键轨道的线性组合与整体硬度（η）值之间的关系。化合物1 ~ 3、4 ~ 6和7 ~ 9的超共轭异构体效应、整体硬度（η）和零点能之间存在直接关系。较硬的轴向构象具有较大的超共轭异位效应和零点能量值，比相应的平伏构象更稳定。
The correlations between the global hardness (η), hyperconjugative anomeric effect, Pauli exchange-type repulsions, electrostatic model associated with dipole–dipole interaction and structural parameters in 2-fluorotetrahydropyran, -thiopyran, -selenopyran (1–3) and their chloro- (4–6) and bromo-analogs (7–9) were investigated by means of the conventional and range-corrected functionals and natural bond orbital (NBO) interpretation. By deletion of the HC-exo-AE and HC-endo-AE, the equatorial conformations of compounds 1–9 become more stable than their corresponding axial forms, revealing that anomeric relationships in compounds 1–9 have the hyperconjugative anomeric effect origins while the electrostatic model associated with dipole–dipole interaction does not play a determining role on the variations of the anomeric relationships in these compounds. The anomeric relationships in compounds 1–3 have no Pauli exchange-type repulsions origin, but it has a significant impact on the conformational preferences in compounds 4–6 and 7–9. A canonical molecular orbital interpretation was conducted to investigate the correlations between the linear combinations of natural bond orbitals in the HOMOs, LUMOs and the global hardness (η) values. There is a direct relationship between the hyperconjugative anomeric effect, global hardness (η) and zero-point energies in compounds 1–3, 4–6 and 7–9. The harder axial conformations with the greater hyperconjugative anomeric effect and zero-point energy values are more stable than their corresponding equatorial forms.