Does a halogen bond require positive potential on the acid and negative potential on the base?
Does a halogen bond require positive potential on the acid and negative potential on the base?
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DOI：
10.1039/d3cp00379e
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发表时间：
2023-02-20
影响因子：
3.3
通讯作者：
Scheiner，Steve
中科院分区：
文献类型：
--
作者：
Scheiner，Steve
通常认为，卤素键（XB）的形成需要与路易斯酸上的σ或π空穴相关的正静电电位区域与碱的负电位相互作用，要么是孤对，要么是π键区域。模型系统的量子计算表明这是不必要的。在碱上放置吸电子取代基可使其孤对或π键区电位的符号反转为正，但碱仍可参与路易斯酸的带正σ空穴的XB。在某些情况下，相反的情况也是可能的，因为带负电的σ-空穴可以与碱的负孤对区形成XB。尽管有这些经典的库仑斥力，总的静电相互作用在这些xb中是有吸引力的，尽管只是弱的。令人惊讶的是，这些键的强度对配对分子的变化不敏感。例如，即使靠近的酸的σ-孔的深度范围很广，XB对带正电位的碱的强度变化也很小。
It is usually expected that formation of a halogen bond (XB) requires that a region of positive electrostatic potential associated with a σ or π-hole on the Lewis acid will interact with the negative potential of the base, either a lone pair or π-bond region. Quantum calculations of model systems suggest this not to be necessary. The placement of electron-withdrawing substituents on the base can reverse the sign of the potential in its lone pair or π-bond region to positive, and this base can nonetheless engage in a XB with the positive σ-hole of a Lewis acid. The reverse scenario is also possible in certain circumstances, as a negatively charged σ-hole can form a XB with the negative lone pair region of a base. Despite these classical Coulombic repulsions, the overall electrostatic interaction is attractive in these XBs, albeit only weakly so. The strengths of these bonds are surprisingly insensitive to changes in the partner molecule. For example, even a wide range in the depth of the σ-hole of the approaching acid yields only a minimal change in the strength of the XB to a base with a positive potential.