NMR Experiments on Acetals. Part 55. Conformational Equilibria in 5-Ethenyl-, 5-Ethynyl- and 5-Cyclopropyl- 1,3-Dioxane

✍ Scribed by M. Anteunis; R. Camerlynck; R. De Waele

• Publisher: Wiley (John Wiley & Sons)
• Year: 2010
• Weight: 488 KB
• Volume: 83
• Category: Article
• ISSN: 0037-9646
• DOI: 10.1002/bscb.19740831111

✦ Synopsis

Abstract

Quantitative conformational data are reported for the title compounds (Table I), as obtained from an extensive ^1^H‐NMR study at several temperatures. Identification of the Me‐5 signals (axial or equatorial) at T < T~C~ could be achieved by spectral comparison with the corresponding anancomerized 2‐Me‐derivatives. The latter were finally related by chemical means to either r‐2‐Me‐cis‐5‐Me‐5‐Et‐1,3‐dioxane or r‐2‐Me‐trans‐5‐Me‐5‐Et‐1,3‐dioxane. The configurations of the latter two compounds were ascertained by specific long range study, established by nmdr.

The conformational results show that in typical apolar solvents the unsaturated substituents slightly prefer the equatorial position with respect to Me, but the axial position in freon‐21. This may be the result of counteracting electrostatic (or dipolar) and steric contributions, but special solvent effects of undisclosed nature govern the conformational picture.