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Configuration and conformation of substituted azetidines
Author(s) -
Kingsbury C. A.,
Soriano D. S.,
Podraza K. F.,
Cromwell N. H.
Publication year - 1982
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570190116
Subject(s) - chemistry , steric effects , ring (chemistry) , nitrogen inversion , zwitterion , chemical shift , ring flip , stereochemistry , nuclear overhauser effect , cis–trans isomerism , coupling constant , nuclear magnetic resonance spectroscopy , crystallography , ring size , alkyl , molecule , nitrogen , organic chemistry , physics , particle physics
Studies of compounds such as 1‐cyclohexyl‐2‐carbomethoxy‐4‐methylazetidine by H‐1 nmr coupling constants, nuclear Overhauser effects, C‐13 steric shifts, and N‐15 nmr support the revised assignment of configuration for cis/trans isomers in a series of N ‐alkyl substituted azetidines. The trans isomer displayed spectral characteristics consistent with a planar or nearly planar ring. The cis isomer favors a puckered ring, with major substituents at C‐2 and C‐4 equatorial. Compounds lacking the C‐4 methyl are also puckered. Puckering angles are estimated. In contrast, trans ‐1‐cyclohexyl‐2‐carboxy‐4‐methylazetidine (a zwitterion) prefers a puckered ring, possibly implicating the time averaged effect of nitrogen inversion on ring shape. The N‐15 spectra show a large difference in chemical shift between cis and trans isomers of the azetidines, although analogous aziridines show an even larger difference.