Departament de Química Inorgànica and Institut de Química Teòrica i Computacional, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
Nat Chem. 2011 Apr;3(4):323-30. doi: 10.1038/nchem.1004. Epub 2011 Mar 6.
Alkane molecules are held together in the crystal state by purportedly weak homonuclear R-H···H-R dihydrogen interactions. In an apparent contradiction, the high melting points and vaporization enthalpies of polyhedranes in condensed phases require quite strong intermolecular interactions. Two questions arise: 'How strong can a weak C-H···H-C bond be?' and 'How do the size and topology of the carbon skeleton affect these bonding interactions?' A systematic computational study of intermolecular interactions in dimers of n-alkanes and polyhedranes, such as tetrahedrane, cubane, octahedrane or dodecahedrane, showed that attractive C-H···H-C interactions are stronger than usually thought. We identified factors that account for the strength of these interactions, including the tertiary nature of the carbon atoms and their low pyramidality. An alkane with a bowl shape was designed in the search for stronger dihydrogen intermolecular bonding, and a dissociation energy as high as 12 kJ mol⁻¹ is predicted by our calculations.
烷烃分子在晶体状态下通过据称较弱的同核 R-H···H-R 双氢键相互作用结合在一起。在一个明显的矛盾中，多面体在凝聚相中具有较高的熔点和蒸发热，这需要相当强的分子间相互作用。由此产生了两个问题：“弱的 C-H···H-C 键能有多强？”和“碳骨架的大小和拓扑结构如何影响这些键合相互作用？”对 n-烷烃和多面体（如四面体、立方烷、八面体或十二面体）二聚体的分子间相互作用的系统计算研究表明，具有吸引力的 C-H···H-C 相互作用比通常认为的要强。我们确定了这些相互作用强度的因素，包括碳原子的叔性质及其低三角锥度。为了寻找更强的双氢分子间键合，设计了一种具有碗状形状的烷烃，我们的计算预测其离解能高达 12 kJ mol⁻¹。
