13C and1H nuclear magnetic resonance spectroscopy of C-19 and 6β-methyl substituted steroids: long-range shift effects in conformational analysis
作者:
Katherine Násfay Scott,
Thomas Harold Mareci,
期刊:
Canadian Journal of Chemistry
(NRC Available online 1979)
卷期:
Volume 57,
issue 1
页码: 27-37
ISSN:0008-4042
年代: 1979
DOI:10.1139/v79-005
出版商: NRC Research Press
数据来源: NRC
摘要:
13C and1H nmr spectra were obtained and assigned for nine C-19 substituted cholest-5-enes, three 6β-substituted 19-norcholest-5(10)-enes, and several related steroids.13C chemical shift effects have previously not been studied in either C-19 substituted steroids or in cholest-5(10)-enes. In the present study, substituent effects on the13C chemical shifts of the α, β, γ, and δ carbons were evaluated in detail. Although the substituent in C-19 substituted and 6β-methyl substituted steroids is less rigidly oriented with respect to the rest of the molecule than in ring-substituted steroids, similar shift effects were observed. In cholest-5-enes the observed13C and1H shift effects and the temperature dependence of the13C shifts indicate that the preferred orientation of the C-19 substituent isantito C-1. The relative stabilities of the rotamers can be attributed to the orientation of the C-19 substituent with respect to the double bond. This interpretation is supported by the fact that the preferred orientation of the iodine in 6β-iodomethyl-19-norcholest-5(10)-en-3β-ol has the same spacial relationship with respect to the double bond, i.e.,gaucheto C-5 and C-7.
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