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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
Author(s) -
Yavari Issa
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270140616
Subject(s) - chemistry , racemization , spectral line , crystallography , nmr spectra database , activation energy , nuclear magnetic resonance spectroscopy , stereochemistry , nuclear magnetic resonance , physics , astronomy
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.