Abstract
Conformational studies on 1,2-dimethoxyethane (DME), a monomer model compound of poly(oxyethylene), have been carried out by using NMR technique. The observed temperature dependence of the vicinal coupling constants was analyzed on the basis of the rotational isomeric state scheme. For the C–C bond, the 13CH satellite side bands provide the desired information. Conformational energy Eσ, representing the energy of the gauche state expressed relative to the trans, was found to vary in a range −0.5 to −1.2 kcal mol−1, depending on the solvent system. Values of JT and JG for the vicinal 1H–1H coupling were determined concomitantly: JT=11.4±0.3 and JG=2.3±0.1 Hz. For the rotation about the C–O bond, the vicinal 13C–1H coupling constant associated with the terminal methyl group was studied. Adoption of JG=1.3 Hz leads to an estimate of Eρ=0.8 to 1.1 kcal mol−1 for the energy difference between the gauche and trans states. In these treatments, the neighbor-dependent character of the bond rotation along the chain was rigorously taken into account. The values of Eσ and Eρ derived for the polymer are comparable with those of DME. The results are compared with those reported previously by Viti et al. and Mastuzaki et al.
Similar content being viewed by others
Article PDF
References
A. Abe and J. E. Mark, J. Am. Chem. Soc., 98, 6468 (1976).
A. Abe, T. Hirano, and T. Tsuruta, Macromolecules, 12, 1092 (1979).
A. Abe, I. Ando, K. Kato, and I. Uematsu, Polym. J., 13, 1069 (1981).
J. E. Mark and P. J. Flory, J. Am. Chem. Soc., 87, 1415 (1965).
J. E. Mark and P. J. Flory, J. Am. Chem. Soc., 88, 3702 (1966).
P. J. Flory, “Statistical Mechanics of Chain Molecules,” Interscience, New York, N.Y., 1969.
Y. Sasanuma, dissertation for master degree, Tokyo Institute of Technology, 1982.
H. S. Gutowsky, G. G. Belford and P. E. McMahon, J. Chem. Phys., 36, 3353 (1962).
T. M. Connor and K. A. McLauchlan, J. Phys. Chem., 69, 1888 (1965).
K. Matsuzaki and H. Ito, J. Polym. Sci., Polym. Phys. Ed., 12, 2507 (1974).
V. Viti, P. L. Indovina, F. Podo, L. Radics, and G. Némethy, Mol. Phys., 27, 541 (1974).
R. J. Abraham and G. Gatti, J. Chem. Soc., Sect. B, 961, (1969).
A. Abe and K. Tasaki, to be published.
In the previous paper,1 we adopted notation σ′ to designate the statistical weight for the C–O bond. In this paper primes are used to distinguish the type of vicinal coupling constants. To avoid confusion, σ′ is replaced by ρ.
In a more sophisticated scheme, torsional potentials are often expressed as a series of cosine terms such as A proper combination of E1, E2 and E3 (with higher terms neglected) should yield a given gauche–trans energy difference. For the purpose at hand, however, introduction of a simple parameter Δ E should suffice. With the expression given in the text, the threefold character of the potential is retained. For the introduction of the Δ E term, the present treatment differs from our previous calculation and that of F. Podo et al.15
F. Podo, G. Némethy, P. L. Indovina, L. Radics, and V. Viti, Mol. Phys., 27, 521 (1974).
U. W. Suter and P. J. Flory, Macromolecules, 8, 765 (1975).
Gutowsky’s original prescription7 involves simultaneous determination of Eσ, JG, and J′T+J″G by the nonlinear least-squares treatment. A similar attempt on the present data sometimes yields, fictitious values for the coupling constants. For elucidation of a reliable set of parameters, a more elaborate scheme is required.
The rule is generally valid for 1,2-disubstituted ethanes XCH2CH2X, in which the size and polarity of X are moderate.19 Validity of such a semiempirical criterion has been confirmed by the FPT-INDO calculation as well (unpublished results).
R. J. Abraham and G. Gatti, J. Chem. Soc. Sect. B, 961 (1969).
N. Sheppard and J. J. Turner, Proc. R. Soc. London, Ser. A, 252, 506 (1959).
J. L. Marshall, “Carbon-Carbon and Carbon–Proton NMR Couplings,” Verlag Chemie International, 1983.
P. E. Hansen, Progress in NMR Spectroscopy, 14, 175 (1981).
R. J. Abraham and K. G. R. Pachler, Mol. Phys., 7, 165 (1963).
R. J. Abraham and E. Bretschneider, “Internal Rotation in Molecules,” W. J. Orville-Thomas, Ed., John Wiley and Sons, 1974, Chapter 13.
H. Matsuura and K. Fukuhara, J. Mol. Struct., to be published.
H. Wieser, W. G. Laidlaw, P. J. Kruger, and H. Fuhrer, Spectrochim. Acta, A, 24, 1055 (1968).
T. Kitagawa and T. Miyazawa, Bull. Chem. Soc. Jpn., 41, 1967 (1968).
J. P. Perchard, J. Mol. Struct., 6, 457 (1970).
K. Oyanagi and K. Kuchitsu, Bull. Chem. Soc. Jpn., 51, 2237 (1978).
E. E. Astrup, Acta Chem. Scan., Ser. A, 33, 655 (1979).
J. Kugler, E. W. Fischer, M. Peuscher, and C. D. Eisenbach, Makromol. Chem., 184, 2325 (1983).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Tasaki, K., Abe, A. NMR Studies and Conformational Energy Calculations of 1,2-Dimethoxyethane and Poly(oxyethylene). Polym J 17, 641–655 (1985). https://doi.org/10.1295/polymj.17.641
Issue Date:
DOI: https://doi.org/10.1295/polymj.17.641