Myths about the proton. The nature of H+ in condensed media.
Myths about the proton. The nature of H+ in condensed media.
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DOI：
10.1021/ar400064q
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发表时间：
2013-11-19
影响因子：
18.3
通讯作者：
Reed, Christopher A.
中科院分区：
文献类型：
--
作者：
Reed, Christopher A.
最近的研究告诉我们，大多数质子化的物种显然不能很好地由一个简单的质子加成来表示。当H+、HA、H2 A+等被写在化学式、化学方程式和酸催化反应中时，氢离子（“质子”）的实际性质是什么？在凝聚介质中，H+必须被溶剂化，并且几乎总是二配位的-如具有H（OEt 2）2+阳离子和弱配位阴离子的可分离的双二乙基醚盐所示。甚至碳正离子，如质子化的烯烃有显着的C-H-阴离子氢键，使活性质子双配位的字符。氢键无处不在，特别是当涉及酸时。与在水、冰和蛋白质中发现的正常的、不对称的O-H-O氢键相反，当存在强酸时，通常出现短、强、低势垒（SSLB）氢键。不寻常的低频IR νOHO带是SSLB氢键的良好指示剂，奇怪的是，与低势垒氢键中H+附近的基团振动相关的带通常从IR光谱中消失。书写H3 O+（本征离子），就像教科书中经常出现的那样，似乎比H+在水中的电离酸更现实。然而，这也是对H（aq）+的不切实际的描述。H5 O2+阳离子（Zundel离子）中的二水合H+变得更接近，但仍然无法合理化H（aq）+的所有实验和计算数据。研究人员不了解H（aq）+的红外吸收的宽范围，称为“连续宽吸收”（cba）。理论没有再现cba，但它似乎是运动速度比IR时标快的离域质子的特征。这对涉及H（aq）+的反应机制意味着什么？在过去的十年中，碳硼烷酸H（CHB 11 Cl 11）一直是已知最强的布朗斯特酸。(It现在被氟化类似物H（CHB 11 F11）超越。碳硼烷酸的强度足以在室温下使烷烃质子化，产生H2和碳正离子。它们使氯代烷烃质子化，产生二烷基氯离子，后者衰变为碳阳离子。通过部分质子化氧鎓阳离子，它们尽可能接近传说中的H4 O2+离子，这在计算机之外是可以实现的。
Recent research has taught us that most protonated species are decidedly not well represented by a simple proton addition. What is the actual nature of the hydrogen ion (the “proton”) when H+, HA, H2A+ etc. are written in formulae, chemical equations and acid catalyzed reactions? In condensed media, H+ must be solvated and is nearly always di-coordinate – as illustrated by isolable bisdiethyletherate salts having H(OEt2)2+ cations and weakly coordinating anions. Even carbocations such as protonated alkenes have significant C-H---anion hydrogen bonding that gives the active protons two-coordinate character. Hydrogen bonding is everywhere, particularly when acids are involved. In contrast to the normal, asymmetric O-H---O hydrogen bonding found in water, ice and proteins, short, strong, low-barrier (SSLB) H-bonding commonly appears when strong acids are present. Unusually low frequency IR νOHO bands are a good indicator of SSLB H-bonds and curiously, bands associated with group vibrations near H+ in low-barrier H-bonding often disappear from the IR spectrum. Writing H3O+ (the Eigen ion), as often appears in textbooks, might seem more realistic than H+ for an ionized acid in water. However, this, too, is an unrealistic description of H(aq)+. The dihydrated H+ in the H5O2+ cation (the Zundel ion) gets somewhat closer but still fails to rationalize all the experimental and computational data on H(aq)+. Researchers do not understand the broad swath of IR absorption from H(aq)+, known as the “continuous broad absorption” (cba). Theory has not reproduced the cba, but it appears to be the signature of delocalized protons whose motion is faster than the IR timescale. What does this mean for reaction mechanisms involving H(aq)+? For the past decade, the carborane acid H(CHB11Cl11) has been the strongest known Brøsted acid. (It is now surpassed by the fluorinated analogue H(CHB11F11).) Carborane acids are strong enough to protonate alkanes at room temperature, giving H2 and carbocations. They protonate chloroalkanes to give dialkylchloronium ions, which decay to carbocations. By partially protonating an oxonium cation, they get as close to the fabled H4O2+ ion as can be achieved outside of a computer.
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影响因子：
5.6
作者：
Cox RA
通讯作者：
Cox RA
影响因子：
16.6
作者：
Avelar, Amy;Tham, Fook S.;Reed, Christopher A.
通讯作者：
Reed, Christopher A.
影响因子：
16.6
作者：
Kueppers, Torsten;Bernhardt, Eduard;Lehmann, Christian W.
通讯作者：
Lehmann, Christian W.
影响因子：
15
作者：
Koppel, IA;Burk, P;Mishima, M
通讯作者：
Mishima, M
DOI：
10.1073/pnas.92.5.1604
发表时间：
1995-02-28
影响因子：
11.1
作者：
FETTER, JR;QIAN, J;FERGUSONMILLER, S
通讯作者：
FERGUSONMILLER, S