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Magnetic shielding of alpha protons by the carbonyl group in cyclohexanones

✍ Scribed by Keith M. Wellman; Frederick G. Bordwell

Publisher: Elsevier Science
Year: 1963
Tongue: French
Weight: 244 KB
Volume: 4
Category: Article
ISSN: 0040-4039
DOI: 10.1016/s0040-4039(01)90898-6

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✦ Synopsis

The original observation that axial protons in cyclohexane and pyran systems absorb at higher p.m.r. fields than their equatorial counterpartsla has been followed by numerous similar reports, and has been stated in the form of a general rule.lb In contrast, Williamson and Johnson noted that the axial 3a proton in 38-acetoxy-5a-cholestan-Z-one resonates at a lower field than the comparable 38 equatorial proton in its ja-acetoxy epimer.2 We wish to report a number of other instances where axial protons alpha to the carbonyl group in cyclohexanones absorb at lower field than their equatorial counterparts (Table I). l(a) R. U. Lemieux, R. K. Kullnig, H. J. Bernstein and W. G. Schneider, 2. &. m. &., & 6098 f19.58); (b) L. M. Jackman, flApplication of Nuclear Magnetic Resonance Spectroscopy to Organic Chemistry", Pergamon Press, 1959, P. 116.

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