NMR studies and conformational energy calculations of 1,2-dimethoxyethane and poly(oxyethylene).

Tasaki Kenzabu, Abe Akihiro

doi:10.1295/polymj.17.641

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 E_σ, 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 J_T and J_G for the vicinal ¹H–¹H coupling were determined concomitantly: J_T=11.4±0.3 and J_G=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 J_G=1.3 Hz leads to an estimate of E_ρ=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 E_σ and E_ρ 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.

NMR studies and conformational energy calculations of 1,2-dimethoxyethane and poly(oxyethylene).

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