1.5-di-tert.-butyl-1.5-diphenyl-pentatetraen

Helical orbitals and circular currents in linear carbon wires

“…† Such systems have been reported in the literature and may hold promise for further functionalization at the chemically stable phenyl rings. [52][53][54][55][56] The possibility of systematically splitting the helical frontier orbitals of cumulenes by chemical design opens the Fig. 3 Optimized molecular structure and Newman projections along each C-N axis (approximate).…”

Coarctate and Möbius: The Helical Orbitals of Allene and Other Cumulenes

“…The shortest even [ n ]­cumulene, allene, is a common starting material in organic syntheses; the variety of synthesized derivatives is immense. − Successful syntheses of the longer even [ n ]­cumulenes are sparse, most likely due to their high reactivity. Still a number of [4]­cumulenes − and a few metallo-[6]­cumulenes − have been reported. In comparison, odd [ n ]­cumulenes have been synthesized and characterized up to [9]­cumulene, − while polyynes have been made with up to 44 carbon atoms. − Ingenious strategies are being developed to further stabilize these otherwise highly reactive molecules, including protection with a rotaxane ring, and growth of carbon wires inside carbon nanotubes; similar strategies may hold great promise for stabilizing even [ n ]­cumulenes.…”

“…The α,ω-disubstituted, chiral [ n ]­cumulenes attracted much attention in early synthetic work, and a number of allenes and [4]­cumulenes were successfully synthesized and characterized, including the aforementioned α,ω-dimethyl substituted species, which have C 2 symmetry, studied by Hendon et al (Scheme , right). ,,− Early studies had a particular focus on the chiroptical properties of allene. Though the researchers active in the field probably did not realize at the time that some of the allenes have helical orbitals, they certainly were aware that the chirality and reduced symmetry of the molecules had implications for their electronic structure.…”