891 Pure Appl. Chem., Vol. 82, No. 4, pp. 891–904, 2010. doi:10.1351/PAC-CON-09-09-04 © 2010 IUPAC, Publication date (Web): 13 March 2010 Toward carbyne: Synthesis and stability of really long polyynes* Rik R. Tykwinski 1,2,‡ , Wesley Chalifoux 2 , Sara Eisler 3 , Andrea Lucotti 4 , Matteo Tommasini 4 , Daniele Fazzi 5 , Mirella Del Zoppo 4 , and Giuseppe Zerbi 4 1 Institute for Organic Chemistry, Friedrich-Alexander-University, Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany; 2 Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada; 3 Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada; 4 Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy; 5 Center for NanoScience and Technology CNST IIT@PoliMi, via Pascoli 70/3, 20133 Milan, Italy Abstract: Molecules composed of sp-hybridized carbon chains (polyynes) are the simplest of the known conjugated organic oligomers. In comparison to their counterparts such as poly- acetylene and polydiacetylene, however, the formation of polyynes has traditionally posed a difficult synthetic challenge. In particular, there is no reliable method to form end-capped polyethynylene, and monodisperse polyynes have therefore been assembled. As a result, structure–property relationships for shorter polyynes have been relatively well established in recent years, while extension of these trends toward longer polyynes has remained a difficult task. Using the Fritsch–Buttenberg–Wiechell (FBW) rearrangement, the formation of diynes through decaynes has become possible and has provided a unique chance to explore the phys- ical characteristics of conjugated polyyne chains. This paper highlights recent advances in the synthesis of extended polyynes, as well as interesting aspects of their NMR, Raman, and UV/vis spectroscopic analyses. These synthetic achievements offer the opportunity to predict some of the properties of the carbon allotrope carbyne. In particular, a set of X-ray crystallo- graphic analyses of t-Bu end-capped polyynes (tBu[n]) shows a definitive experimental trend in reduced bond-length alternation (BLA). Keywords: alkylidene carbenes; alkynes; carbyne; conjugated oligomers; Peierls distortion; polyynes; Raman spectroscopy. INTRODUCTION Many aspects of modern science depend on the chemistry and properties of the various forms of pure carbon, including diamond (sp 3 -hybridized carbon) and graphite/graphene (sp 2 -hybridized carbon), as well as the more recent studies of fullerenes and nanotubes [1]. Extending this trend to sp-hybridized carbon leads to the compound/material often referred to as carbyne [2]. The existence, structure, and properties of carbyne have been a topic of some discussion [3–5], but this account will not attempt to *Pure Appl. Chem. 82, 757–1063 (2010). An issue of reviews and research papers based on lectures presented at the 13 th International Symposium on Novel Aromatic Compounds (ISNA-13), 19–24 July 2009, Luxembourg City, Luxembourg on the theme of aromaticity. ‡ Corresponding author