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Control of Helix Sense by Composition of Chiral–Achiral Copolymers of N ‐Propargylbenzamides
Author(s) -
Tabei Junichi,
Shiotsuki Masashi,
Sato Takahiro,
Sanda Fumio,
Masuda Toshio
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200401009
Subject(s) - copolymer , helix (gastropod) , polymer , monomer , polymer chemistry , polymerization , materials science , chirality (physics) , enantiomer , composition (language) , crystallography , chemistry , stereochemistry , organic chemistry , physics , chiral symmetry , ecology , linguistics , philosophy , quantum mechanics , snail , nambu–jona lasinio model , biology , quark
Abstract N‐ Propargylbenzamides 1 – 7 were polymerized with (nbd)Rh + [η 6 ‐C 6 H 5 B − (C 6 H 5 ) 3 ] to afford polymers with moderate molecular weights ( M n = 26 000–51 000) in good yields. The 1 H NMR spectra demonstrated that the polymers have fairly stereoregular structures (81–88 % cis ). The optically active polymers, poly( 1 ) and poly( 2 ), were proven by their intense CD signals and large optical rotations to adopt a stable helical conformation with an excess of one‐handed screw sense when heated in CHCl 3 or toluene. The sign of Cotton effect could be controlled by varying the content in the copolymers of either chiral bulky 1 and achiral nonbulky 3 , or chiral nonbulky 2 and achiral bulky 7 . The smaller the pendant group in the copolymerization of achiral monomers with 1 , the more easily did the preferential helical sense change with the copolymer composition. However, the copolymers of chiral nonbulky 2 and achiral nonbulky 3 did not change the helical sense, irrespective of the composition. The free energy differences between the plus and minus helical states, as well as the excess free energy of the helix reversal, of those chiral–achiral random copolymers were estimated by applying a modified Ising model.

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