Formation of Curvature Subunit of Carbon in Combustion

Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C5–C18 that are online produced in the flame of acetylene–cyclopentadiene–oxygen and in situ captured by C60 or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C20H10. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process.碳材料领域普遍存在曲率结构（例如富勒烯（fullerenes）、巴基碗（buckyl bowls）、碳纳米管（carbon nanotubes）以及洋葱碳（carbon onions）），但传统的C2加成（C2-addition）机制无法阐明当前诸如燃烧这类化学物理过程中，由五边形碳环引发的碳曲率形成机制。本文报道了一系列完整的新生含五边形碳环的C5–C18碳簇：这些碳簇在乙炔-环戊二烯-氧气火焰中在线生成，可被C60原位捕获，或作为多环芳烃被捕获，以此阐明C20H10弯曲亚基的生长过程。我们提出了一种涉及C1取代（C1-substitution）与C2加成的机制，用以阐释碳材料中曲率结构的形成，并以由五个六元环完全包裹单个五元环的典型弯曲分子为例进行说明。本机制得到了经X射线晶体学与核磁共振（NMR）表征的中间体的支持，并通过实验验证了在具有商业应用价值的燃烧过程中，可控合成弯曲分子的可行性。