Abstract
The conformational equilibrium of the purely isotactic oligomers of chloral, CH3O[CH(CCl3)O]nR (R=CH3, C2H5, COCH3; 3≤n≤8), has been investigated by means of 500 MHz dynamic 1H NMR spectroscopy in solution. The oligomers assumed the structure of a stable 4/1 helix consisting of repeated gauche(−)-skew(+) (g̅s) or skew(−)-gauche(+) (s̅g) sequences along the acetal backbone. The interconversion between the right-handed (gs)n and left-handed (sg)n helices was slow enough for the NMR spectroscopy to distinguish clearly the two states. ΔH and ΔS between the two helical states of CH3O[CH(CCl3)O]6C2H5 were determined as 0.498 kcal lmo−1 and 0.238 cal K−1 mol−1, respectively, and those of CH3O[CH(CCl3)O]6COCH3 as −0.988 kcal mol−1 and 1.40 cal K−1 mol−1. The ΔH values were consistent with the results from molecular mechanics calculations. The activation energy for the helix-sense inversion (ΔG≠) has been found to depend on the degree of polymerization, n. The values were 8.2, 12.7, 16.4, and 19.6 kcal mol−1 for the symmetrical oligomers (R=CH3) with n=3, 4, 5, and 6, respectively. The linear increase of ΔG≠ with n suggested that it should be possible to resolve the symmetrical “meso” oligorners higher than the hexamer into the optical antipodes at room temperature based entirely on conformational asymmetry; this supposition has been confirmed by chiral resolution using the HPLC technique with (+)-poly(triphenylmethyl methacrylate) as stationary phase.
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L. S. Corley and O. Vogl, Polym. Bull., 3, 211 (1980).
G. D. Jaycox and O. Vogl, Polym. Commun., 30, 354 (1989).
W. J. Harris and O. Vogl, J. Macromol. Sci.-Chem., A26, 1067 (1989).
W. J. Harris and O. Vogl, J. Macromol. Sci.-Chem., A26, 1083 (1989).
G. D. Jaycox and O. Vogl, Makromol. Chem., Rapid Commun., 11, 61 (1990).
Y. Okamoto, K. Suzuki, K. Ohta, K. Hatada, and H. Yuki, J. Am. Chem. Soc., 101, 4763 (1979).
Y. Okamoto, I. Okamoto, and H. Yuki, J. Polym. Sci., Polym. Lett. Ed., 19, 451 (1981).
R. J. M. Nolte, A. J. M. van Beijnen, and W. Drenth, J. Am. Chem. Soc., 96, 5932 (1974).
P. C. J. Kamer, R. J. M. Nolte, and W. Drenth, J. Am. Chem. Soc., 110, 6818 (1988).
Y. Ito, E. Ihara, and M. Murakami, Angew. Chem. Int. Ed. Engl., 31, 1509 (1992).
Y. Okamoto, H. Mohri, T. Nakano, and K. Hatada, J. Am. Chem. Soc., 111, 5952 (1989).
L. S. Corley, Ph. D. Dissertation, University of Massachusetts, 1979.
O. Vogl, J. Macromol. Sci., Pure Appl. Chem., A29, 1085 (1992).
M. M. Green, C. Andreola, B. Muñoz, M. P. Reidy, and K. Zero, J. Am. Chem. Soc., 110, 4063 (1988).
S. Lifson, C. Andreola, N. C. Peterson, and M. M. Green, J. Am. Chem. Soc., 111, 8850 (1989).
O. Vogl, F. Xi, F. Vass, K. Ute, T. Nishimura, and K. Hatada, Macromolecules, 22, 4658 (1989).
K. Ute, T. Nishimura, K. Hatada, F. Xi, F. Vass, and O. Vogl, Makromol. Chem., 191, 557 (1990).
K. Ute, K. Oka, Y. Okamoto, K. Hatada, F. Xi, and O. Vogl, Polym. J., 23, 1419 (1991).
K. Ute, K. Oka, and K. Hatada, manuscript in preparation.
K. Ute, K. Hirose, H. Kashimoto, K. Hatada, and O. Vogl, J. Am. Chem. Soc., 113, 6305 (1991).
O. Vogl, H. C. Miller, and W. H. Sharkey, Macromolecules, 5, 658 (1972).
J. Zhang, G. D. Jaycox, and O. Vogl, Polymer, 29, 707 (1988).
K. Hatada, K. Ute, T. Nakano, F. Vass, and O. Vogl, Makromol. Chem., 190, 2217 (1989).
K. Ute, N. Miyatake, T. Asada, and K. Hatada, Polym. Bull., 28, 561 (1992).
Y. Okamoto, S. Honda, I. Okamoto, H. Yuki, S. Murata, R. Noyori, and H. Takaya, J. Am. Chem. Soc., 103, 6971 (1981).
N. L. Allinger and Y. H. Yuh, Quantum Chemistry Program Exchange, 12, 395 (1980).
A. Abe, K. Tasaki, K. Inomata, and O. Vogl, Macromolecules, 19, 2707 (1986).
R. R. Ernst, G. Bodenhausen, and A. Wokaun, “Principles of Nuclear Magnetic Resonance in One and Two Dimensions,” Clarendon Press, Oxford, 1987, p 516.
G. K. Hamer, F. Balza, N. Cyr, and A. S. Perlin, Can. J. Chem., 56, 3109 (1978).
R. Yamada and I. Ando, Polym. Prepr. Jpn., 32, 835 (1983).
K. Ute, K. Oka, M. Kashiyama, K. Hatada, F. Xi, and O. Vogl, Makromol. Chem., 192, 35 (1991).
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Ute, K., Hirose, K., Kashimoto, H. et al. Helix-Inversion Equilibrium of Isotactic Chloral Oligomers in Solution. Polym J 25, 1175–1186 (1993). https://doi.org/10.1295/polymj.25.1175
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DOI: https://doi.org/10.1295/polymj.25.1175
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