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首页> 外文期刊>Chemistry: A European journal >Schlenk's Early 'Free' Carbanions
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Schlenk's Early 'Free' Carbanions

机译：舒伦克的早期“免费”碳负离子

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摘要

Nearly a century ago, Schlenk published the syntheses and isolation of two msot remarkable and unstable complexes: crystalline [Ph_3C~-] [Me_4N~+] and [PhCH_2~-][Me_4N~+]. The crystal structure of the first complex contains a "free" Ph_3C~- ion, which displays the expected planar trigonal geometry at its central carbon atom. The phenyl groups are not orientated in the typical propeller arrangement, but instead display various orientations with respect to the molecular plane. These orientations can be directly related to the extent of cahrge delocalization and correlate well with other structural characteristics related to charge delocalization. The crystal structure also shows a network of C-H~(delta+)...C~(delta-) and C-H...pi interactions. Only C-H...pi interactions to the most negative charged phenyl rings are observed. The absolute Bronsted acidity of Me_4N~+ is calculated by the G2(MP2) method (287.7 kcal mol~(-1)) and is compared to the calcualted acidity of Me_4P~+ (268.4 kcal mol~(-1)). On this basis, the pK_a value for Me_4N~+ is estimated at 29.6. This makes the existence, and especially Schlenk's early isolation, of the "free" carbanions [Ph_3C~-] [Me_4N~+] and [PhCH_2~-] [Me_4N~+] quite noteworthy.
机译：大约一个世纪前，Schlenk发表了两种杂色显着且不稳定的配合物的合成和分离：晶体[Ph_3C〜-] [Me_4N〜+]和[PhCH_2〜-] [Me_4N〜+]。第一配合物的晶体结构包含“游离” Ph_3C-离子，其在其中心碳原子处显示出预期的平面三角几何形状。苯基在典型的螺旋桨布置中没有取向，而是相对于分子平面显示出各种取向。这些取向可以直接与大分子离域的程度有关，并且与与电荷离域的其他结构特征很好地相关。晶体结构还显示出C-H〜（δ+）... C〜（δ-）和C-H ... pi相互作用的网络。仅观察到C-H ... pi与最带负电的苯环的相互作用。 Me_4N〜+的绝对布朗斯台德酸度通过G2（MP2）方法（287.7 kcal mol〜（-1））计算，并与Me_4P〜+的计算酸度（268.4 kcal mol〜（-1））进行比较。在此基础上，Me_4N〜+的pK_a值估计为29.6。这使得“自由”碳负离子[Ph_3C〜-] [Me_4N〜+]和[PhCH_2〜-] [Me_4N〜+]的存在，尤其是Schlenk的早期分离非常值得注意。

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