α to Carbonyl Group
13α,14α- and 13β,14β-Steroids
Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
A new 13C NMR method based on solvent effects allows the identification of carbon atoms α to a carbonyl group. With a simple change in solvent from CDCl3 to CDCI3-dioxane (1:4), the 13C absorption for all earbons except those α to the carbonyl group in the compounds under study were displaced to lower field by 0.2-0.5 ppm. The α-carbon absorptions either remained unchanged or were shifted to higher field by ca 0.1 ppm. The validity of the method has been checked on compounds with fully assigned 13C NMR spectra (trans-decalones and steroids). Moreover, no modification of these solvent shifts due to the presence of other common functional groups (double bond or OH) was observed. This new technique, together with existing ‘classical’ methods (‘off-resonance’ spectra, substituent effects) enables the complete interpretation of the 13 C NMR spectra of five cis-decalins and cis-decalones to be made. The spectra of three cis-hydrindanones which have not been previously described were also fully interpreted.The same method allows the complete spectral assignment of the 13C NMR spectra of six steroids of unnatural configuration in the 13α,14α- and 13β,14β-androstane series, for which no data were previously available.
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