As counterintuitive as it might seem, in aprotic media, electron transfer (ET) from strong Lewis basic anions, particularly F^–, OH^–, and CN^–, to certain π-acids (πA) is not only spectroscopically evident from the formation of paramagnetic πA^•– radical anions and πA^2– dianions, but also thermodynamically justified because these anions’ highest occupied molecular orbitals (HOMOs) lie above the π-acids’ lowest unoccupied molecular orbitals (LUMOs) creating negative free energy changes (ΔG°_ET < 0). Depending on the relative HOMO and LUMO energies of participating anions and π-acids, respectively, the anion-induced ET (AIET) events take place either in the ground state or upon photosensitization of the π-acids. The mild basic and charge-diffuse anions with lower HOMO levels fail to trigger ET, but they often form charge transfer (CT) and anion−π complexes. Owing to their high HOMO levels in aprotic environments, strong Lewis basic anions, such as F^– enjoy much greater ET driving force (ΔG°_ET) than mild and non-basic anions, such as iodide. In protic solvents, however, the former become more solvated and stabilized and lose their electron donating ability more than the latter, creating an illusion that F^– is a poor electron donor due to the high electronegativity of fluorine. However, UV–vis, EPR, and NMR studies consistently show that in aprotic environments, F^– reduces essentially any π-acid with LUMO levels of −3.8 eV or less, revealing that contrary to a common perception, the electron donating ability of F^– anion is not dictated by the electronegativity of fluorine atom but is a true reflection of high Lewis basicity of the anion itself. Thus, the neutral fluorine atoms with zero formal charge and F^– anion have little in common when it comes to their electronic properties. The F^– anion can also legitimately act as a Brønsted base when the proton source has a pK_a lower than that of its conjugate acid HF (15), not the other way around, and ET from F^– to a poor electron acceptor is not thermodynamically feasible. While there is no shortage of indisputable evidence and clear-cut thermodynamic justifications for ET from F^– and other Lewis basic anions to various π-acids in aprotic solvents, because of the aforesaid misconception, it had been posited that F^– perhaps formed diamagnetic Meisenheimer complexes via nucleophilic attack, deprotonated an aprotic solvent DMSO against an insurmountably high pK_a (35) leading to a π-acid reduction, or formed [F^–/πA^•+] complexes via a thermodynamically prohibited oxidation of π-acids. Unlike AIET, however, none of these hypotheses was thermodynamically viable nor supported by any experimental evidence.

中文翻译：

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阴离子诱导的电子转移

由于违反直觉的，因为它看起来，在非质子传递媒体，从强路易斯碱性阴离子，特别是F的电子转移（ET）^-，OH ^-和CN ^- ，某些π共酸（πA）不仅从形成光谱明显顺磁性πA ^{• -}自由基阴离子和πA ^2-二价阴离子，而且热力学合理的，因为这些阴离子最高占据分子轨道（候牟司）位于该π酸以上最低未占分子轨道（LUMOS）创建负自由能变化（Δ ģ ° _ET<0）。分别取决于参与的阴离子和π酸的相对HOMO和LUMO能量，阴离子诱导的ET（AIET）事件在基态或π酸的光敏作用下发生。具有较低HOMO含量的温和碱性和电荷扩散阴离子无法触发ET，但它们通常形成电荷转移（CT）和阴离子-π络合物。由于其在非质子环境中的较高HOMO含量，强力的Lewis碱性阴离子（例如F ^–）比温和非碱性阴离子（例如碘化物）享有更大的ET驱动力（ΔG ° _ET）。但是，在质子传递溶剂中，前者变得比后者更溶剂化和稳定，并且失去了更多的供电子能力，从而产生了一种幻想，即F ^–由于氟的高电负性，它是一个不良的电子供体。但是，UV-VIS，EPR和NMR研究一致表明，在质子惰性的环境中，F ^-本质上降低了任何π共酸与LUMO能级-3.8电子伏特或更小，表明相反到共同的感知，给电子的F能力^–阴离子不是由氟原子的电负性决定的，而是对阴离子本身高路易斯碱性的真实反映。因此，零形式电荷和F中性氟原子^-负离子有什么共同之处，当涉及到他们的电子特性。在F ^-阴离子也可以合法地充当当质子源具有p布朗斯台德碱ķ_一个比其共轭酸HF（15）低，反之亦然，并且从F ^–到不良电子受体的ET在热力学上不可行。虽然对于ET从F无争的证据和明确的热力学理据不足^-以及其它路易斯碱性阴离子各种π酸，因为上述的误解，在非质子溶剂，它已被假定那个F ^-或许形成抗磁迈森海梅通过亲核攻击形成复合物，使质子惰性溶剂DMSO去质子化，以克服无法克服的高p K _a（35）导致π酸还原，或形成[F ^– /πA ^•+通过热力学上禁止的π酸的氧化而形成络合物。但是，与AIET不同，这些假设在热力学上都不可行，也没有任何实验证据支持。