Calculation of the relative basicity of three α,ω‐diphenylpolyenes with trifluoroacetic acid
Calculation of the relative basicity of three α,ω‐diphenylpolyenes with trifluoroacetic acid
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三氟乙酸计算三种α、β-二苯基多烯的相对碱度
DOI：
10.1002/poc.4412
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发表时间：
2022
影响因子：
1.8
通讯作者：
Biffinger, Justin C.
中科院分区：
文献类型：
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作者：
Masthay, Mark B.;McLean, Jack B.;Santos, Ariana L.;Pirlo, Russell K.;Biffinger, Justin C.
线性多烯是一类重要的化合物，含有两个或多个交替的碳碳双键和单键，主要溶于有机非极性溶剂。然而，事实证明，通过实验确定未取代多烯的相对碱度在实践中具有挑战性，因为此类研究需要将非极性多烯有机溶剂混合物与高浓度的中等极性有机酸混合。在本研究中，我们使用计算和实验方法计算了反式1,4-二苯基-1,3-丁二烯（DPB）、全反式-1,6-二苯基-1,3,5-己三烯（DPH）和全反式-1,8-二苯基-1,3,5,7-辛四烯（DPO）在正己烷或苯溶剂中与三氟乙酸（TFAH）的潜在质子化位点。使用 6-311 + G (d,p) 基组和 B3LYP 交换相关函数进行的密度泛函理论 (DFT) 计算预测，任一苯环的碳原子 α 是最有可能的质子化位点。我们的计算表明，在气相以及苯和正庚烷溶剂中，DPP 的碱度随着多烯部分 (DPO > DPH >> DPB) 长度的增加而增加。与这些计算预测一致，苯和己烷中 DPB、DPH 和 DPO 的质子化实验速率与计算的碱度趋势一致。动态光散射数据证实这些反应是相分离的，导致 TFAH 和两种溶剂之间形成乳液；这些相分离使实际反应速率的规范变得复杂。最后，GC-MS 和 NMR 数据证实 DPB 和 DPH 质子化的粗产物是 DPB 和 DPH 二聚体的混合物。与此形成鲜明对比的是，DPO 没有形成二聚体，而是形成了一种未鉴定的单体三氟乙酸酯加成产物。
Linear polyenes are an important class of compounds containing two or more alternating carbon‐carbon double and single bonds that are soluble primarily in organic non‐polar solvents. However, determining the relative basicity of unsubstituted polyenes experimentally has proven to be challenging in practice because such studies require mixing non‐polar polyene‐organic solvent mixtures with high concentrations of moderately polar organic acids. In this study, we used both computational and experimental approaches to calculate potential sites of protonation oftrans‐1,4‐diphenyl‐1,3‐butadiene (DPB), alltrans‐1,6‐diphenyl‐1,3,5‐hexatriene (DPH), and alltrans‐1,8‐diphenyl‐1,3,5,7‐octatetraene (DPO) with trifluoroacetic acid (TFAH) in bothn‐hexane or benzene solvents. Density functional theory (DFT) calculations with a 6‐311 + G (d,p) basis set and the B3LYP exchange correlation functional predict that the carbon atoms α to either phenyl ring are the most likely sites of protonation. Our calculations indicate that the basicities of the DPPs increase with increasing length of the polyene moiety (DPO > DPH >> DPB) in the gas phase and in both benzene andn‐heptane solvents. Consistent with these computational predictions, the experimental rates of protonation of DPB, DPH, and DPO in benzene and hexane were consistent with the calculated basicity trends. Dynamic light scattering data confirmed that these reactions were phase separated resulting in emulsions between TFAH and both solvents; these phase separations complicated specification of the actual reaction rates. Finally, GC‐MS and NMR data confirm that the crude products from the protonation of DPB and DPH were mixtures of DPB and DPH dimers. In significant contrast, DPO did not form dimers but rather an unidentified monomeric trifluoroacetate addition product.