13C and 1H nuclear magnetic resonance spectroscopy of C-19 and 6β-methyl substituted steroids: long-range shift effects in conformational analysis

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Abstract
13C and 1H NMR spectra were obtained and assigned for 9 C-19 substituted cholest-5-enes, 3 6.beta.-substituted 19-norcholest-5(10)-enes, and several related steroids. Substituent effects on the 13C chemical shifts of the .alpha., .beta., .gamma. and .delta. C were evaluated in detail. Although the substituent in C-19 substituted and 6.beta.-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 observed 13C and 1H shift effects and the temperature dependence of the 13C shifts indicate that the preferred 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 I in 6.beta.-iodomethyl-19-norcholest-5(10)-en-3.beta.-ol has the same spacial relationship with respect to the double bond, i.e., gauche to C-5 and C-7.

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