Ressonancia magnetica nuclear dinamica de alguns derivados ciclo-decanicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

This work is concerned with the spectroscopic study of 8,9-seco-lanostanes and 8,9-seco-7,9-cyclo-lanostanes using 1 and 2 dimensional NMR spectroscopy. From lanosteroI 1, we have obtained four 8,9-seco-lanostane derivatives and two 8,9-seco- 7,9-cyclo-lanostane derivatíves. Two of these Ianostane derivatives have not! been previously reported in the literature. The 3b-acetoxy-9-hydroxy.5a-8,9-seco-lanostan-8-one (monoalcohol 6) and 3b-acetoxy-8,9-dihydroxy-5a-8,9-seco-lanostane (diol 8), undergo slow intramoIecular exchange processes in the NMR tinte scale. MM2 empirical method was used to calculate the energies of the two prefered conformers of monoalcohoI 6 and their popuIations. The interconversion barriers were 48,72 and 55,41 KJ/mol and the population ratiÍo was 1:21. From these results, we could to explain the presence of only one set af carbon signals at low temperatures correspanding to the signals of the most stable conformer of 6. For diol 8 the MM2 calculations suggested the existence of 4 conformers, but only two of them had detectable populatios in a 1:2 ratio with 47,28 and 48,59 KJ/mol energy barriers between them. At low temperatures, the superimposed spectra of the two conformers were too complex to interprete. However, the carbon-13 NMR spectrom of diol 8, obtained at 90°C, showed only one set of carbon signals indicating a fast interconversion process. The signal were assigned to the structure. The spectra of two additional cyclodecane derivatives (diketone 4 and keto-olefin 9), and the two lanostane derivatives containing 5 and 7 membered fused rings (alcohol 7 and ab insaturated ketone 10) revealed that these compounds were conformationally rigid at room temperature. Finally, this study brought new contributions to the slow intramolecular exchange processes in cyclodecane derivatives

ASSUNTO(S)

ressonancia magnetica nuclear

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