Screw sense of polyisocyanides

Beijnen, A.J.M. van; Nolte, Roeland J. M.; Drenth, W.; Hezemans, Alfons M. F.

doi:10.1016/0040-4020(76)80097-x

Cited by 66 publications

(55 citation statements)

References 9 publications

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“…Theoretical calculations of electronic CD, followed by comparison with the observed CD of certain helical polymers, such as 2 76 and N-alkylated optically active poly(p-benzamide) (32), 49 were performed to predict their preferred-handed helical senses in solution. The helical senses of poly(N-butynylamide)s having various optically active side chains (33a,b) 77 and an optically active poly(phenylacetylene) bearing achiral galvinoxyl pendants (34) prepared by helixsense-selective polymerization 78 have also been postulated by comparing the observed CD spectra with simulated ones.…”

Section: Helical Structure Determination Of Liquid Crystalline Helicamentioning

confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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During the last decade, remarkable progress in developing synthetic helical polymers with a controlled helical sense has been achieved. However, the exact helical structures of most of the already prepared synthetic helical polymers remain unsolved. In this review, the recent progress in the synthesis of helical polymers and their structural determination, including helical pitch and handedness based on X-ray diffraction and spectroscopic measurements, together with high-resolution atomic force microscopy, is described. Polymer Journal (2010) 42, 3-16; doi:10.1038/pj.2009 Keywords: atomic force microscopy; circular dichroism; helical polymer; helical structure; X-ray diffractionThe helix is a unique structure as observed in nature from microscopic to macroscopic levels and is inherently chiral. Inspired by biological helices, such as DNA and proteins, chemists have been challenged to synthesize helical polymers with a controlled helical sense that aims not only to mimic biological helical structures but also to develop chiral materials for the separation of enantiomers and asymmetric catalysis. [1][2][3][4][5][6][7][8][9][10][11][12] The history of synthetic helical polymers with optical activity extends back to the 1960s when Pino and Lorenzi 13 investigated the structural and chiroptical properties of isotactic vinyl polymers prepared by the polymerization of a-olefins bearing optically active substituents. Although helical polyolefins are totally dynamic in nature and consist of short helical segments separated by frequently occurring helical reversals among disordered, random coil conformations, 14 this study was significant in the field of synthetic helical polymers, from which a number of helical polymers have been synthesized.On the basis of the pioneering studies by Nolte et al., 15 Okamoto et al. 16 and Green et al., 17 the existing synthetic helical polymers that exhibit an optical activity solely because of their macromolecular helicity can be classified into two categories with respect to their helix inversion barriers, that is, static and dynamic helical polymers (Figure 1). 9,12 Optically active helical polymers, such as poly(triphenylmethyl methacrylate) (1), 16 poly(t-butyl isocyanide) (2) 15 and polychloral (3), 18 have a sufficiently high helix inversion barrier and belong to the family of static helical polymers. Therefore, these helical polymers with either a right-or left-handed helix can be prepared by the helix-sense-selective polymerization of the corresponding achiral monomers using chiral catalysts or initiators under kinetic control. On the other hand, dynamic helical polymers, such as polyisocyanates (8) 17 and polysilanes (9), 19 possess a very low helix inversion barrier.As a consequence, they consist of interconvertible right-and lefthanded helical segments separated by rarely occurring helical reversals, as demonstrated by Green et al.,6,20,21 so that a preferred-handed helical conformation can be induced in the presence of a small amount of chiral residues at the pendant 6 or ter...

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Section: Helical Structure Determination Of Liquid Crystalline Helicamentioning

confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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“…1) to be a stable form of the secondary structure with bulky substituents. 9 There is an ongoing debate concerning this topic, however, with some claiming 10 that the assignment of helicity as was originally made 11,12 was erroneous, while others call into question whether the 4 1 helix is the most likely secondary structure. 13,14 There is a lack of very direct unquestionable evidence in both camps, and what seems certain is that the conformation a given poly(isocyanide) forms and the stability that this secondary structure has depends greatly on the substituent.…”

Section: Introductionmentioning

confidence: 99%

“…13,14 There is a lack of very direct unquestionable evidence in both camps, and what seems certain is that the conformation a given poly(isocyanide) forms and the stability that this secondary structure has depends greatly on the substituent. [11][12][13][14] The situation is complicated further by the possibility of stereoirregularity arising from syn and anti conformers of the imine, 15 be what may the backbone conformation. The slow equilibration of conformations of a nonsterically encumbered aromatic poly (isocyanide) has been observed experimentally, and was interpreted as a slow interconversion as an asformed 4 1 helix to a more open s-trans zigzag conformation which can adopt a helical twist along its length.…”

Section: Introductionmentioning

confidence: 99%

Long‐range effects of chirality in aromatic poly(isocyanide)s

Amabilino

Serrano

Sierra

et al. 2006

J. Polym. Sci. A Polym. Chem.

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The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral “information” can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd–even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161–3174, 2006

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“…The property of chirality appeared from the resolution of poly(tertbutyliminomethylene) into its optically active enantiomers [6 ]. Also, the circular dichroism spectra of these enantiomers support a helical configura tion [7] . The screw sense of the enantiomers has been assigned [7].…”

Section: Introductionmentioning

confidence: 99%

“…Also, the circular dichroism spectra of these enantiomers support a helical configura tion [7] . The screw sense of the enantiomers has been assigned [7]. In continuation of our earlier, mainly kinetic study of the polymer ization [4 ] , we now presentam ore detailed mechanism which is in agreement with the reactivity of coordinated isocyanides, as well as with the stereo chemistry of ligand substitution at nickel(II).…”

Section: Introductionmentioning

confidence: 99%