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首页> 外文期刊>Chemistry: A European journal >Enhanced Li~+ Binding Energies in Alkylbenzene Derivatives:The Scorpion Effect
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Enhanced Li~+ Binding Energies in Alkylbenzene Derivatives:The Scorpion Effect

机译：烷基苯衍生物中增强的Li〜+结合能：蝎子效应

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The gas-phase lithium cation basicities(LCBs;Gibbs free energy of binding)of ethyl-,n-butyl-,and n-heptylbenzene have been measured by Fourier transform ion cyclotron resonance(FT-ICR) mass spectrometry.The structures of the corresponding complexes and their relative stabilities were investigated through the use of B3LYP/6-311G~+(3df,2p)//B3LYP/6-31G(d)density functional theory calculations.For n-butylbenzene and n-beptylbenzene,the most stable adducts correspond to pi complexes in which the alkyl chain coils toward the aromatic ring to favor its interaction with the metal cation.The extra stabilization provided by the flexible alkyl chain polarized by the charge on Li~+ is named the "scorpion effect".Conversely,these coiled conformations are among the least stable in the neutral system;they are not all stationary points on the potential-energy surface.The formation of complexes with a coiled alkyl chain leads to a significant enhancement of the Li~+ bonding energies(LBEs),which are approximately 20-30 Kj mol~-1 higher than those calculated for alkylbenzene pi complexes in which an uncoiled chain remains distant from the cation and thus minimizes the scorpion effect.This enhancement is less significant when LCBs are concerned,because the scorpion effect is entropically disfavored.There is very good agreement between the experimental Li~+ gas-phase basicities and the calculated values,provided that the statistical distribution of the conformers present in the gas phase is taken into account in this calculation.
机译：通过傅里叶变换离子回旋共振（FT-ICR）质谱法测量了乙基，正丁基和正庚基苯的气相锂阳离子碱度（LCBs;吉布斯结合自由能）。通过B3LYP / 6-311G〜+（3df，2p）// B3LYP / 6-31G（d）密度泛函理论计算研究了相应的配合物及其相对稳定性。对于正丁基苯和正丁基苯，稳定的加合物对应于pi络合物，其中烷基链朝芳香环盘旋，以促进其与金属阳离子的相互作用。由Li〜+上的电荷极化的柔性烷基链提供的额外稳定性被称为“蝎子效应”。相反，这些盘绕构象在中性系统中是最不稳定的;它们并不是势能表面上的所有固定点。带有盘绕烷基链的配合物的形成导致Li〜+键合能的显着增强（ LBE），这是ap比烷基苯pi络合物的计算值高约20-30 Kj mol〜-1，烷基酚pi络合物的未卷曲链仍远离阳离子，从而使蝎子效应最小化。当涉及LCB时，这种增强作用不那么显着，因为蝎子效应是熵的在实验中，Li〜+气相碱度与计算值之间有很好的一致性，前提是该计算中要考虑气相中存在的构象异构体的统计分布。

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