Linear acetylenic carbon

Linear acetylenic carbon (LAC), also called carbyne, is an allotrope of carbon that has the chemical structure[1] -(C≡C)n- as a repeating chain.[2]

The carbon atoms in this form are each linear in geometry with sp orbital hybridisation: it is a polymer with alternating single and triple bonds. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of diamond, the hardest known material.[3] The existence of carbyne itself as a carbon allotrope is controversial, as the properties and synthetic methods seem consistent with generation of fullerenes.[4] However, polyalkyne oligomers called polyynes as substructures of larger compounds are well known and actively researched as a substitute.[5] Carbyne chains of over 300 carbons have been prepared and appear to be reasonably stable as long as the terminal alkynes on the chain are capped rather than having a free acetylenic H atom.[6] The analysis in this study specifically demonstrated that the result was a carbyne-like structure rather than a fullerene.

An analysis of a synthesized linear carbon allotrope found it to have a cumulene electronic structure—sequential double bonds along an sp-hybridized carbon chain—rather than the alternating triple–single pattern of linear carbyne.[7]

References

  1. ^ Heimann, R.B.; Evsyukov, S.E.; Kavan, L. (Eds.) (1999). Carbyne and Carbynoid Structures. Physics and Chemistry of Materials with Low-Dimensional Structures. 21. p. 452. ISBN 0-7923-5323-4. 
  2. ^ Baughman, R. H. (2006). "Dangerously Seeking Linear Carbon". Science 312: 1009–1110. doi:10.1126/science.1125999. 
  3. ^ Itzhaki, L.; Altus, E.; Basch, H.; Hoz, S. (2005). "Harder than Diamond: Determining the Cross-Sectional Area and Young's Modulus of Molecular Rods". Angew. Chem. Int. Ed. 44: 7432–7435. doi:10.1002/ange.200502448. PMID 16240306. 
  4. ^ Kroto, H. (November 2010). "Carbyne and other myths about carbon". RSC Chemistry World. http://www.rsc.org/chemistryworld/Issues/2010/November/CarbyneOtherMythsAboutCarbon.asp. 
  5. ^ Chalifouxa, W. A.; Tykwinsk, R. R. (2009). "Synthesis of extended polyynes: Toward carbyne". Comptes Rendus Chimie 12 (3): 341–358. doi:10.1016/j.crci.2008.10.004. 
  6. ^ Lagow, R. J.; Kampa, J. J.; Han-Chao Wei, H.-C.; Scott L. Battle, S. L.; John W. Genge, J. W.; Laude, D. A.; Harper, C. J.; Bau, R.; Stevens, R. C.; Haw. J. F.; Munson, E. (1995). "Synthesis of Linear Acetylenic Carbon: The "sp" Carbon Allotrope". Science 267 (5196): 362–367. Bibcode 1995Sci...267..362L. doi:10.1126/science.267.5196.362. 
  7. ^ Xue, K.-H.; Tao, F.-F.; Shen, W.; He, C.-J.; Chen, Q.-L.; Wu, L.-J.; Zhu, Y.-M. (2004). "Linear carbon allotrope – carbon atom wires prepared by pyrolysis of starch". Chemical Physics Letters 385 (5–6): 477–480. Bibcode 2004CPL...385..477X. doi:10.1016/j.cplett.2004.01.007. 
sp3 forms
sp2 forms
sp forms
Linear acetylenic carbon
mixed sp3/sp2 forms
other forms
C1 • C2 • C3 • C8
related