环[18]碳

环[18]碳或环十八-1,3,5,7,9,11,13,15,17-九炔是碳的同素异形体之一，化学式为C
18，几乎不溶于水。^[1]它是一种环碳和多炔，由十八个碳原子以单叁键交替构成环。环[18]碳是预测能够热力学稳定最小的环[n]碳，理论应变能为72 kcal/mol。^[2][3]

环［18］碳
识别
CAS号	126487-09-0  Y
PubChem	14940714
ChemSpider	74015635
SMILES	C1#CC#CC#CC#CC#CC#CC#CC#CC#C1
性质
化学式	C18
摩尔质量	216.19 g·mol⁻¹
密度	1.38±0.1 g·cm−3（20 °C）[1]
若非注明，所有数据均出自标准状态（25 ℃，100 kPa）下。

历史和制备

早在1991年，便有人对环[18]碳的结构进行预测，并进行过有关计算，^[4]但其合成却在2019年才被IBM和牛津大学的联合团队^[5]通过环丁酮结构的数个位点进行电化学脱羰基反应制得：^[6]

环碳的合成

它也可由C₁₈Br₆的脱溴反应制得。^[7]

性质

IBM研究人员发现，环[18]碳的电子结构（英语：electronic structure）由交替的单叁键构成，而非累计双键结构，它在理论上是一种半导体。^[6]

在该化合物中，C—C键的键长为1.36 Å，C≡C的键长为1.20 Å。^[5]

参考文献

1. Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (© 1994-2019 ACD/Labs). Retrieved from SciFinder. [2019-8-21]
2. George A. Adamson; Charles W. Rees. Towards the total synthesis of cyclo[n]carbons and the generation of cyclo[6]carbon. J. Chem. Soc., Perkin Trans. 1. 1996, (13): 1535–1543. doi:10.1039/P19960001535.
3. François Diederich; Yves Rubin; Carolyn B. Knobler; Robert L. Whetten; Kenneth E. Schriver; Kendall N. Houk; Yi Li. All-Carbon Molecules: Evidence for the Generation of Cyclo[18]carbon from a Stable Organic Precursor. Science. 1989-09-08, 245 (4922): 1088–1090. Bibcode:1989Sci...245.1088D. PMID 17838807. doi:10.1126/science.245.4922.1088.
4. Parasuk, Vudhichai; Almlof, Jan; Feyereisen, Martin W. The [18] all-carbon molecule: cumulene or polyacetylene?. Journal of the American Chemical Society. 1991, 113 (3): 1049–1050. ISSN 0002-7863. doi:10.1021/ja00003a052.
5. Kaiser, Katharina; Scriven, Lorel M.; Schulz, Fabian; Gawel, Przemyslaw; Gross, Leo; Anderson, Harry L. An sp-hybridized molecular carbon allotrope, cyclo[18]carbon. Science. 2019-08-15 [2019-08-21]. doi:10.1126/science.aay1914. （原始内容存档于2019-08-21）.
6. Castelvecchi, Davide. Chemists make first-ever ring of pure carbon. Nature. 2019-08-15 [2019-08-16]. doi:10.1038/d41586-019-02473-z. （原始内容存档于2019-08-16） （英语）.
7. Lorel M. Scriven, Katharina Kaiser, Fabian Schulz, Alistair J. Sterling, Steffen L. Woltering, Przemyslaw Gawel, Kirsten E. Christensen, Harry L. Anderson, Leo Gross. Synthesis of Cyclo[18]carbon via Debromination of C 18 Br 6. Journal of the American Chemical Society. 2020-07-29, 142 (30): 12921–12924 [2020-08-22]. ISSN 0002-7863. doi:10.1021/jacs.0c05033. （原始内容存档于2020-10-17） （英语）.

拓展阅读

• Sen, Sabyasachi; Seal, Prasenjit; Chakrabarti, Swapan. Explicit role of dynamical and nondynamical electron correlations on broken symmetry inC_4N+2clusters. Physical Review B. 2006, 73 (24). ISSN 1098-0121. doi:10.1103/PhysRevB.73.245401.
• Feyereisen, Martin; Gutowski, Maciej; Simons, Jack; Almlöf, Jan. Relative stabilities of fullerene, cumulene, and polyacetylene structures for C_n:n=18–60. The Journal of Chemical Physics. 1992, 96 (4): 2926–2932. ISSN 0021-9606. doi:10.1063/1.461989.
• Murphy, Veronica L.; Farfan, Camille; Kahr, Bart. Chiroptical structure-property relations in cyclo[18]carbon and its in silico hydrogenation products. Chirality. 2018, 30 (4): 325–331. ISSN 0899-0042. doi:10.1002/chir.22817.