title: Accordion-like oscillation of contracted and stretched helices of polyacetylenes synchronized with the restricted rotation of side chains.
abstract: A chiral substituted acetylene, (s)-2-octyl propiolate, was stereoregularly polymerized using a catalyst, [Rh(nbd)Cl]2, at 40 °C in methanol to give the corresponding helical polymer, Ps2OcP. The changes of (1)H and (13)C NMR spectra in line shapes and splitting patterns were consistently interpreted in terms of restricted rotation around the ester O-*C bond, ~O-*C(ε)H(ε)(R)~, R = a branched CH(ε)3 in the ester side chains rather than the helix inversion with the aid of a 3-site jump model. Three peaks due to the branched methyl H(ε) proton and its C(η) carbon observed at 0 °C suggested the formation of three rotamers called A, B, and C, based on the presence of the contracted helix and stretched helix forms that have an intrinsic helical pitch. Furthermore, an accordion-like helix oscillation (HELIOS) along the main chain axis was proposed to explain the temperature dependence spectral changes observed in (1)H and (13)C NMR, UV-vis, and circular dicromism (CD) spectra. The temperature dependence UV-vis and CD spectra of Ps2OcP corroborate the presence of contracted and stretched one-handed helix sense polymers in solution in which the helical pitches and their persistence lengths depend on the temperature.
authors: Department of Applied Chemistry, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido 050-8585, Japan.
authors: Yoshiaki
authors: Y
authors: Yoshida
authors: Yasuteru
authors: Y
authors: Mawatari
authors: Asahi
authors: A
authors: Motoshige
authors: Ranko
authors: R
authors: Motoshige
authors: Toshifumi
authors: T
authors: Hiraoki
authors: Manfred
authors: M
authors: Wagner
authors: Klaus
authors: K
authors: Müllen
authors: Masayoshi
authors: M
authors: Tabata
mesh_terms: D002384:Catalysis; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry; D053279:Polyynes / Q000138:chemical synthesis* / Q000737:chemistry; D012399:Rotation
chemical_list: D009942:Organometallic Compounds; D053279:Polyynes