Aggregation of asphaltenes in petroleum crude oil is a well-known and ongoing problem for petroleum production. Asphaltenes aggregate even in situations where polycyclic aromatic hydrocarbon (PAH) model compounds do not, which implies that there is more to the phenomenon than just π-stacking. Half-pancake bonds involving stable radical PAH have been hypothesized to contribute to asphaltene aggregation (Zhang, Y.; Energy Fuels 2020, 34 (8), 9094−9107). We report density functional theory calculations on half-pancake bonding in asphaltene model compounds. Pancake and half-pancake bonds can be viewed as multi-center generalizations of (common) two-electron covalent bonds and (rare) odd-electron bonds, respectively. In the absence of other effects, we find negligible half-pancake bonding between radical PAH and neutral nonradical PAH. Introducing heteroatoms can produce modestly strong donor-acceptor half-pancake-type interactions. Our results suggest that half-pancake bonding alone is too weak and too rare to drive asphaltene aggregation. However, interactions between stable organic radicals, heteroatoms, and polar groups may contribute to aggregation.

中文翻译：

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沥青质中的半薄饼粘合

石油原油中沥青质的聚集是石油生产中众所周知且持续存在的问题。即使在多环芳烃 (PAH) 模型化合物不聚集的情况下，沥青质也会聚集，这意味着该现象不仅仅是 π 堆积。已经假设涉及稳定自由基 PAH 的半薄饼键有助于沥青质聚集。张，Y.; 能源燃料 2020 , 34 (8), 9094−9107)。我们报告了沥青质模型化合物中半薄饼键合的密度泛函理论计算。薄饼和半薄饼键可以分别视为（常见）双电子共价键和（稀有）奇电子键的多中心概括。在没有其他影响的情况下，我们发现自由基 PAH 和中性非自由基 PAH 之间的半薄饼键可以忽略不计。引入杂原子可以产生适度强的供体-受体半薄饼型相互作用。我们的结果表明，单独的半薄饼粘合太弱且太稀有，无法驱动沥青质聚集。然而，稳定的有机自由基、杂原子和极性基团之间的相互作用可能会导致聚集。