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A dynamic nuclear magnetic resonance spectroscopic study of conformational properties of 1,3-dioxepane and 4,4,7,7-tetramethyl-1,3-dioxepane

✍ Scribed by Issa Yavari

Publisher: John Wiley and Sons
Year: 1980
Tongue: English
Weight: 336 KB
Volume: 14
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.1270140616

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✦ Synopsis

Abstract

The 251 MHz ^1^H and the natural abundance 63.1 MHz ^13^C NMR spectra of 1,3‐dioxepane (1) and 4,4,7,7‐tetramethyl‐1,3‐dioxepane (2) have been investigated over the temperature range of 5 to −180 °C. While the spectra of 1 show no dynamic NMR effect, compound 2 exists in solution as a 1:1 mixture of a symmetrical (C~2~) twist‐chair and its mirror image conformation. The free energy barrier for the conformational racemization of 2 is 43 kJ mol^−1^ (10.3 kcal mol^−1^). Interconversion paths between various conformations of 2 are discussed. Compound 1 is suggested to have a symmetrical (C~2~) twist‐chair conformation which is rapidly pseudorotating via a chair conformation to achieve a time averaged symmetry of C~2v~, even at −180 °C.

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