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NMR experiments on acetals—XXV: Conformational energy for the chair-twist interconversion of the 1,3-dioxane system

✍ Scribed by M. Anteunis; G. Swaelens

Publisher
John Wiley and Sons
Year
1970
Tongue
English
Weight
422 KB
Volume
2
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Trans‐4‐t‐Bu‐6‐R‐1,3‐dioxanes (R = Me, Pr^i^ and __cyclo__hexyl) show temperature‐dependent values for ^2^J(H—2) and ^3^J(H—4(6), H—5) in their PMR spectra. This is the result of the presence of twist‐boat conformations. With the aid of typical limit‐values of ^2^J(H—2) for the chair and twist forms, the amount of flexible conformations were determined as a function of temperature (Table 2), allowing the determination of the enthalpy change for chair‐twist interconversion in 1,3‐dioxane itself (6·2 ± 0·3 kcal/mole). Typical values for ^2^J(H—2) were obtained from a study of low temperature spectra and from appropriate model compounds of which 4‐(1′‐adamantyl)‐6‐t‐Bu‐1,3‐dioxane served as the model for a genuine twist form with a twofold axis through C‐2/C‐5.

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