The anomeric effect: the dominance of exchange effects in closed-shell systems
The anomeric effect: the dominance of exchange effects in closed-shell systems
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DOI：
10.1039/c2ob26818c
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发表时间：
2013-01-01
影响因子：
3.2
通讯作者：
da Silva, Clarissa O.
中科院分区：
文献类型：
--
作者：
Bauerfeldt, Glauco F.;Cardozo, Thiago M.;da Silva, Clarissa O.
异头效应的起源一直是一个悬而未决的问题。在Mo证明了超共轭不是异头效应的原因之后[Y. Mo，Nature Chem.，2010，2，666.]，静电相互作用和泡利排斥一直是这场争论的中心。本文将环己烷和2-取代四氢吡喃环上的氟、羟基、氰基和氨基的赤道和轴向异构体的最稳定旋转异构体的总能量分解为它们的基本动力学、静电和交换分量。在这种分配方案中，每个端基异构体中最稳定的旋转异构体之间的总能量的差异与交换组分的差异相关性很好，表明端基异构效应没有静电起源。事实上，异头效应是由交换能。这一建议的异头效应的起源带来了新的见解，一旦纳入，可能会改善定性化学模型。这一新的建议的起源异头效应的几何参数和溶剂化的影响进行了讨论。
The origin of the anomeric effect has remained an open question. After Mo demonstrated that hyperconjugation is not responsible for the anomeric effect [Y. Mo, Nature Chem., 2010, 2, 666.], electrostatic interactions and Pauli repulsions have been at the center of this debate. In this work, the total energies of the most stable rotamers of the equatorial and axial anomers of fluoro, hydroxyl, cyano and amino groups in cyclohexane and 2-substituted tetrahydropyran rings are decomposed into their fundamental kinetic, electrostatic and exchange components. In this partitioning scheme, the differences in the total energies among the most stable rotamers of each anomer correlate very well with the differences in the exchange components, revealing that the anomeric effect has no electrostatic origin. Indeed, the anomeric effect is dominated by the exchange energy. This proposal for the origin of the anomeric effect brings new insights that, once incorporated, may improve qualitative chemical models. Implications of this new proposal for the origin of the anomeric effect on geometric parameters and solvation are also discussed.