Artículos de revistas
Conformational Analysis Of Trans-2-halocyclohexanols And Their Methyl Ethers: A 1h Nmr, Theoretical And Solvation Approach
Registro en:
Journal Of Physical Organic Chemistry. , v. 16, n. 1, p. 27 - 33, 2003.
8943230
10.1002/poc.565
2-s2.0-0037231117
Autor
Freitas M.P.
Tormena C.F.
Rittner R.
Abraham R.J.
Institución
Resumen
The conformational equilibria of trans-1-methoxy-2-chloro- (1), trans-1-methoxy-2-bromo- (2) and trans-1-methoxy-2-iodocyclohexane (3), and their corresponding alcohols (4-6), were studied through a combined method of NMR, theoretical calculations and solvation theory. They can be described in terms of the axial-axial and equatorial-equatorial conformations, taking into account the main rotamers of each of these conformations. From the NMR experiments at 183 K in CD2Cl2-CS2, it was possible to observe proton H2 in the ax-ax and eq-eq conformers separately for 1 and 2, but not for 3, which gave directly their populations and conformer energies. In the alcohols the proportion of the ax-ax conformer was too low to be detected by NMR under these conditions. Those HH couplings together with the values at room temperature, in a variety of solvents allowed the determination of the solvent dependence of the conformer energies and hence the vapor state energy difference. The ΔE (Eax-Eeq) values in the vapor state for 1, 2 and 3 are -0.05, 0.20 and 0.55 kcal mol-1, respectively, increasing to 1.10, 1.22 and 1.41 kcal mol-1 in CD3CN solution (1 kcal = 4.184 kJ). For 4-6 the eq-eq conformation is always much more stable in both non-polar and polar solvents, with energy differences ranging from 1.78, 1.94 and 1.86 kcal mol-1 (in CCl4) to 1.27, 1.49 and 1.54 kcal mol-1 (in DMSO), respectively. Comparison of the hydroxy and methoxy compounds gives the intramolecular hydrogen bonding energy for the alcohols as 1.40, 1.36 and 1.00 kcal mol-1 (in CCl4) for 4, 5 and 6, respectively. Copyright © 2002 John Wiley & Sons, Ltd. 16 1 27 33 Zefirov, N.S., Samoshin, V.V., Subbotin, A.O., Baranenkov, V.I., (1978) Tetrahedron, 34, p. 2953 Carreño, M.C., Carretero, J.C., Ruano, J.L., Rodriguez, J.H., (1990) Tetrahedron, 46, p. 5649 Rockwell, G.D., Grindley, T.B., (1996) Aust. J. Chem., 49, p. 379 Kay, J.B., Robinson, J.B., Cox, B., Polkonja, D., (1970) J. Pharm. Pharmacol., 22, p. 214 Collins, P., Ferrier, R., (1995) Monosaccharides-Their Chemistry and Their Roles in Natural Products, , Wiley: New York Bervelt, J.P., Ottinger, R., Peters, P.A., Reisse, J., Chiurdoglu, G., (1968) Spectrochim. Acta, Part A, 24, p. 1411 Allinger, J., Allinger, N.L., (1958) Tetrahedron, 2, p. 64 Allinger, N.L., Allinger, J., (1958) J. Am. Chem. Soc., 80, p. 5476 Basso, E.A., Kaiser, C., Rittner, R., Lambert, J.B., (1993) J. Org. Chem., 58, p. 7865 Bodot, H., Dicko, D.D., Gounelle, Y., (1967) Bull. Soc. Chim. Fr., p. 870 Freitas, M.P., Tormena, C.F., Rittner, R., (2001) J. Mol. Struct., 570, p. 175 Wolfe, S.J., Campbell, R., (1967) J. Chem. Soc., Chem. Commum., p. 872 Abraham, R.J., Bretschneider, E., (1974) Internal Rotation in Molecules, , Academic Press: London, chapt. 13 Abraham, R.J., Jones, A.D., Warne, M.A., Rittner, R., Tormena, C.F., (1996) J. Chem. Soc., Perkin Trans., 2, p. 533 Abraham, R.J., Tormena, C.F., Rittner, R., (1999) J. Chem. Soc., Perkin Trans., 2, p. 1663 Tormena, C.F., Rittner, R., Abraham, R.J., Basso, E.A., Pontes, R.M., (2000) J. Chem. Soc., Perkin Trans., 2, p. 2054 Freitas, M.P., Rittner, R., Tormena, C.F., Abraham, R.J., (2001) J. Phys. Org. Chem, 14, p. 317 Abraham, R.J., Smith, T.A.D., Thomas, W.A., (1996) J. Chem. Soc., Perkin Trans., 2, p. 1949 Frisch, M.J., Trucks, C.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Zakrzewski, V.G., Pople, J.A., (1998) Gaussian 98, , Gaussian: Pittsburgh, PA Abraham, R.J., Grant, G.H., Haworth, I.S., Smith, P.E., (1991) J. Comput.-Aided Mol. Des., 5, p. 21 Zefirov, N.S., Gurvich, L.G., Shashkov, A.S., Krimer, M.Z., Vorob'eva, E.A., (1976) Tetrahedron, 32, p. 1211 Epiotis, N.D., (1973) J. Am. Chem. Soc., 95, p. 3087 Craig, N.C., Chen, A., Suh, K.H., Klee, S., Mellau, G.C., Winnewisser, B.P., Winnewisser, M., (1997) J. Am. Chem. Soc., 119, p. 4789 Senderowitz, H., Fuchs, B., (1997) J. Mol. Struct. (Theochem), 395-396, p. 123 Rablen, P.R., Hoffmann, R.W., Hrovat, D.A., Borden, W.T., (1999) J. Chem. Soc., Perkin Trans., 2, p. 1719 Ganguly, B., Fuchs, B., (2000) J. Org. Chem., 65, p. 558 Li, Z., Fan, K., Wong, M.W., (2001) J. Phys. Chem. A, 105, p. 10890 Wiberg, K.B., Murcko, M.A., Laidig, K.E., Macdougall, P.J., (1990) J. Phys. Chem., 94, p. 6956 Lagowski, J.J., (1976) The Chemistry of Nonaqueous Solvents, 3. , Academic Press: New York Jones, D.C., (1928) J. Chem. Soc., p. 1193 Guss, C.O., Rosenthal, R., (1955) J. Am. Chem. Soc., 77, p. 2549 Sosnovskii, G.M., Astapovich, I.V., (1990) Zh. Org. Khim., 26, p. 911 Bajwa, J.S., Anderson, R.C., (1991) Tetrahedron Lett., 32, p. 3021