Quantitative Assessment by 1D-EXSY NMR of Stereoelectronic Control in Acid-Catalyzed Exchange between Stereoisomeric 2-Methoxy-1,3-dioxanes and Methanol
| العنوان: | Quantitative Assessment by 1D-EXSY NMR of Stereoelectronic Control in Acid-Catalyzed Exchange between Stereoisomeric 2-Methoxy-1,3-dioxanes and Methanol |
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| المؤلفون: | Richard E. Engler, Charles L. Perrin |
| المصدر: | Journal of the American Chemical Society. 119:585-591 |
| بيانات النشر: | American Chemical Society (ACS), 1997. |
| سنة النشر: | 1997 |
| مصطلحات موضوعية: | Chloroform, Stereochemistry, Diastereomer, General Chemistry, Biochemistry, Medicinal chemistry, Catalysis, chemistry.chemical_compound, Colloid and Surface Chemistry, Reaction rate constant, chemistry, Alkane stereochemistry, Methanol, Benzene, Selectivity, Lone pair |
| الوصف: | Rates of acid-catalyzed methoxy exchange between methanol and the three diastereomers of 2-methoxy-4,6-dimethyl-1,3-dioxane (6) were measured in benzene, and the rates for the two cis diastereomers were measured in methanol/chloroform. Rate constants were evaluated using a 1D-EXSY NMR pulse sequence and a weighted linear least squares analysis. Rates of methanol attack on the cationic intermediate (8) show 24-fold axial selectivity in benzene and 9-fold selectivity in methanol/chloroform. A ring-opening mechanism for equatorial exchange can be rejected, since rate constants kea and kae for direct axial/equatorial epimerization are zero. These results demonstrate that antiperiplanar lone pairs are more effective in this system than syn, although the effect is worth no more than 2 kcal/mol. |
| تدمد: | 1520-5126 0002-7863 |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_________::c6d600b28f9bfa678d0b19ea6e5c45b7 https://doi.org/10.1021/ja962808i |
| رقم الأكسشن: | edsair.doi...........c6d600b28f9bfa678d0b19ea6e5c45b7 |
| قاعدة البيانات: | OpenAIRE |
Find this issue from the American Chemical Society | تدمد: | 15205126 00027863 |
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