Synthesis and helical structure of poly (N-butynylamide)s having various side chains, where the Helix is highly affected by the methyl branch and the lactone moiety

N-Butynylamides, (S)-HC CCH2CH2NHCOCH2CH(CH3)CH2CH3 (1), (R)-HC CCH2CH2-NHCOCH2CH(CH3)CH2CH2CH2CH(CH3)(2) (2), (S)-HC CCH2CH2NHCOCH(CH3)CH2CH2CH2CH2CH2CH3 (3),(1S)-HC CCH2CH2NHCOC9H13O2 (4,COC9H13O2 = camphanyl), and HC CCH2CH2NHCOCH2CH2CH2CH2CH3 (5) were polymerized with [(nbd)RhCl](2)-Et3N in CHCl3 to obtain cis-stereoregular poly(N-butynylamide)s [poly(1)-poly(5)]. CD and IR spectroscopic studies revealed that poly(l)-poly(4) having chiral substituents in the side chains took predominantly one-handed helical structure stabilized by intramolecular hydrogen bonds between the pendent amide groups in CHCl3. The helical structure of poly(l)-poly(3) was more stable to heating than that of the corresponding poly (N-propargylamide)s reported so far. In contrast, poly(4) having bulky lactone moieties changed the helical tightness according to temperature. The helical structure of poly(3) having a-methyl branch was much more stable to MeOH addition than that of poly(l) and poly(2) having beta-methyl branch. The persistence length of the poly(N-butynylamide)s was nearly the same as that of poly(N-propargylcarbamate)s, but shorter than that of poly(N-propargylamide)s. Simulation of CD spectra was carried out for helical forms of a poly(N-butynylamide) to specify the asymmetric conformations.