Add time:08/13/2019         Source:sciencedirect.com

Conformation of 1,3-Dimethoxypropane (cas 17081-21-9) has been studied in the gas phase (approximately 120–180°C). Vicinal coupling constants 3JHH and 3JCH determined by 1H and 13C NMR were analysed within the rotational isomeric state approximation. The trans and gauche couplings required in this analysis were set equal to JG = 2.8 Hz and JT = 13.7 Hz for 1HCC1H, and JG = 2.0 Hz and JT + J′G = 16.0 Hz for 13COC1H. The conformational energy parameters of the chain were conventionally defined as Eσ and Eϱ for the gauche state around the CH2CH2 and OCH2 bond, respectively, and Eω for the repulsive second-order interaction (g±g∓) for the OCH2CH2CH2O fragment. The experimental values of the coupling constants were found to be reproduced by a variety of combinations of Eσ and Eω, Eϱ being kept at 1.03 kcal mol−1. Adoption of Eω = 1.97 kcal mol−1, as calculated by a molecular mechanics method, led to Eσ = −0.84 kcal mol−1. Alternatively, by setting Eσ = −0.58 kcal mol−1 as calculated, Eω = 0.40 kcal mol−1. Assuming Eω > 1 kcal mol−1 for the gas phase, a value of Eσ from −0.7 to approximately −0.9 kcal mol−1 was proposed. The conformation, and thus conformational energies, varied quite sensitively with the polarity of the medium. The results were compared with those observed in solution.

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