The anomeric effect on the basis of natural bond orbital analysis
The anomeric effect on the basis of natural bond orbital analysis
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DOI：
10.1039/c3ob40187a
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发表时间：
2013-01-01
影响因子：
3.2
通讯作者：
Freitas, Matheus P.
中科院分区：
文献类型：
--
作者：
Freitas, Matheus P.
异头效应被认为是由于超共轭，静电/空间相互作用或交换效应;因此，关于其实际来源没有普遍的共识。经典的超共轭模型，通常使用自然键轨道（NBO）分析研究，已被任意驳斥，因为它不能解释一些情况下，优选赤道异头比轴向的极性溶液。在这项研究中，超共轭被证明是依赖于介质和NBO分析解释相当好的轴向和赤道2-取代的四氢吡喃（取代基= F，OH，NH 2和CN）在气相和水溶液中的估计量。总的来说，没有理由放弃超共轭模型，因为它在某些系统中起着主导作用的异头效应，而NBO分析再现的基础上的超共轭和刘易斯型贡献的能量配置文件。
The anomeric effect has been assigned as being due to hyperconjugation, electrostatic/steric interactions or exchange effects; thus, there is no general consensus about its actual origin. The classical hyperconjugation model, usually investigated using natural bond orbital (NBO) analysis, has been arbitrarily refuted because it would not explain some cases of the preferred equatorial anomer over the axial one in polar solution. In this study, hyperconjugation was shown to be dependent on the medium and NBO analysis explains quite well the estimated amounts of axial and equatorial 2-substituted tetrahydropyrans (substituents = F, OH, NH2 and CN) both in the gas phase and aqueous solution. Overall, there is no reason to abandon the hyperconjugation model as it plays a dominating role of the anomeric effect in some systems, while NBO analysis reproduces the energetic profiles on the basis of both hyperconjugative and Lewis-type contributions.