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vol.52 número3ORGANOMETALLIC 1,5-BENZODIAZEPINE AND 1,5-BENZODIAZE PINIUM COMPOUNDS: SYNTHESIS, CHARACTERIZATION, X-RAY DIFFRACTION STRUCTURES AND THEORETICAL INVESTIGATION índice de autoresíndice de assuntospesquisa de artigos
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Journal of the Chilean Chemical Society

versão On-line ISSN 0717-9707

Resumo

CONTRERAS, J. GUILLERMO  e  GERLI, LORENA A.. CONFORMATIONAL PREFERENCE OF 4-ETHYL- 6-METHYL-1,3-DITHIANES. J. Chil. Chem. Soc. [online]. 2007, vol.52, n.3, pp.1271-1275. ISSN 0717-9707.  http://dx.doi.org/10.4067/S0717-97072007000300018.

Interconversion reaction of III conformers of 4-ethyl-6-methyl-1,3-dithiane (METDIT) has been studied by means of ab initio methods on the frame of MO theory. Optimized geometries at HF/6-31G** level correlate well with that found for the parent 1,3-dithianefrom an x-ray diffraction study. Both conformers possess similar bond distances, but differ in up 12° in some dihedrals. Conformer I geometry presents the larger distortion from the regular 1,3-dithiane mainly due to difference between angles κ1 and κ2 (ca. 14°). In conformer II this difference is just ca. 3°. The energetics and thermodynamics were obtained with basis sets that include diffuse, polarization functions and electronic correlations at the second-order perturbation Meller Plesset theory. Gas phase thermodynamic predicts II to be in a 98% concentration. Low and medium high polarity solvents seem to exert no influence on the conformers concentrations. Thus the III interconversion reaction is largely displaced to II formation, both in the gas phase and solution. The calculated 1H-NMR data, i.e., chemical shifts and one-bond C-H spin-spin coupling constants are predicted on the basis of the consistent results obtained for the parent 1,3-dithiane. For both conformers reverse Perlin effect takes place at C2 and C5. The C2 - Hax and C2 - Heq bond distances are similar ( ca. 1.092 Å), whereas the C5- Heq are larger than the axial ones yielding smaller 1JC-H coupling constants

Palavras-chave : 4-ethyl-6-methyl-1,3-dithiane; conformational preference; NMR properties.

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