Cyclo [18]carbon (C 18 ), an all-carboatomic molecule formed by 18 sp-hybridized carbon atoms connected in turn, has been widely concerned by many fields such as physics, chemistry, and materials science since it was structurally characterized twice by scanning tunneling microscopy (STM)/atomic force microscopy (AFM) in the condensed phase in 2019 and 2020, respectively. By using atom manipulation on bilayer NaCl on Cu(111) at 5 K, the C 18 molecule was produced for the first time by eliminating carbon monoxides from a cyclocarbon oxide molecule C 18 (CO) 6 in one or more steps, while the latter was realized by dehalogenation of a bromocyclocarbon precursor, C 18 Br 6 . The reaction precursors for preparing C 18 , C 18 (CO) n (n = 6, 4, and 2) and C 18 Br 6 , in the two pioneering experiments are all planar ring structures with high symmetry, and belong to the category of carbon-rich molecules in nature. Although C 18 molecule has been generated and imaged experimentally, due to its high chemical activity, it cannot be stably separated at present. In contrast, the four precursors are stable under ambient conditions, and some of them have even determined by X-ray diffraction. In fact, there is evidence that similar or identical intermediates exist in the gas-phase reaction as early as 1991. Based on this reality, it is more practical, at least at this stage, to explore the physicochemical properties and application prospects of the unusual carbon-rich precursors C 18 (CO) n (n = 6, 4, and 2) and C 18 Br 6 .