Artículos de revistas
Conformational Analysis And Stereoelectronic Effects In Trans-1,2-dihalocyclohexanes: 1h Nmr And Theoretical Investigation
Registro en:
Spectrochimica Acta - Part A: Molecular And Biomolecular Spectroscopy. , v. 61, n. 8, p. 1771 - 1776, 2005.
13861425
10.1016/j.saa.2004.07.007
2-s2.0-17844410384
Autor
Freitas M.P.
Rittner R.
Tormena C.F.
Abraham R.J.
Institución
Resumen
The conformational equilibrium of trans-1,2-difluoro- (1), trans-1,2-dichloro- (2) and trans-1,2-dibromo-cyclohexane (3) was studied through a combined method of NMR, theoretical calculations and solvation theory. The solvent dependence of the JH1,H23 NMR coupling constants together with theoretical calculations allow the direct determination of the conformational equilibria without recourse to model compounds. The coupling constants were obtained with the aid of spectrum simulation, since these symmetric molecules present complex coupling systems. The observed couplings, when analysed by solvation theory and utilising DFT geometries (B3LYP/6-311+G**), gave energy values of Eee - Eaa of 0.10, 0.95 and 1.40 kcal mol-1 in the vapour phase for 1, 2 and 3, respectively, decreasing to -0.63, 0.36 and 0.93 kcal mol-1 in CCl4 and to -1.91, -0.80 and -0.05 kcal mol-1 in DMSO solution. The diaxial preference for all compounds is explained by natural bond orbital (NBO) analysis, which shows important hyperconjugative effects in this conformation. The "gauche effect" for compounds with more electronegative substituents, which are in gauche arrangement in the ee conformation, also plays a relevant role in more polar solvents. © 2004 Elsevier B.V. All rights reserved. 61 8 1771 1776 Abraham, R.J., Rossetti, Z.L., (1973) J. Chem. Soc., Perkin Trans., 2, p. 582 Abraham, R.J., Smith, T.A.D., Thomas, W.A., (1996) J. Chem. Soc., Perkin Trans., 2, p. 1949 Zefirov, N.S., Gurvich, L.G., Shashkov, A.S., Krimer, M.Z., Vorob'Eva, E.A., (1976) Tetrahedron, 32, p. 1211 Zefirov, N.S., Samoshin, V.V., Subbotin, O.A., Baranenkov, V.I., Wolfe, S., (1978) Tetrahedron, 34, p. 2953 Zefirov, N.S., Samoshin, V.V., Subbotin, O.A., Sergeev, N.M., (1981) Zh. Org. Khim., 17, p. 1462 Freitas, M.P., Tormena, C.F., Rittner, R., (2001) J. Mol. Struct., 570, p. 175 Kay, J.B., Robinson, J.B., Cox, B., Polkonja, D., (1970) J. Pharm. Pharmacol., 22, p. 214 Ito, A., Saishoji, T., Kumazawa, S., Chuman, H., (1999) J. Pest. Sci., 24, p. 262 Allinger, J., Allinger, N.L., (1958) Tetrahedron, 2, p. 64 Klaeboe, P., Lothe, J.J., Lunde, K., (1957) Acta Chem. Scand., 11, p. 1677 Bodot, H., Dicko, D.D., Gounelle, Y., (1967) Bull. Soc. Chim. Fr., p. 870 Colborn, R.E., (1990) J. Chem. Ed., 67, p. 438 Abraham, R.J., Bretschneider, E., (1974) Internal Rotation in Molecules, , W.J. Orville Thomas Wiley London 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 Tormena, C.F., Rittner, R., Abraham, R.J., (2002) J. Phys. Org. Chem., 15, p. 211 Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Zakrzewski, V.G., Pople, J.A., (1998) Gaussian98, Revision A.7, , Gaussian, Inc., Pittsburgh, PA E.D. Glendening, J.K. Badenhoop, A.E. Reed, J.E. Carpenter, F.F. Weinhold, Theoretical Chemistry Institute, University of Wisconsin, WI, 1996 (NBO 4.0)Abraham, R.J., Grant, G.H., Haworth, I.S., Smith, P.E., (1991) J. Comp. Aid. Mol. Des., 5, p. 21 Olah, G.A., Nojima, M., Kerekes, J., (1973) Synthesis, p. 780 VNMR 6.1 User Guide: Liquids NMR, , Varian, Palo Alto, CA PCMODEL Version 7.1, , Serena Software, Bloomington, IN, USA Abraham, R.J., Fisher, J., Loftus, P., (1997) Introduction to NMR Spectroscopy, , Wiley New York Reisse, J., Celotti, J.C., Ottinger, R., (1966) Tetrahedron Lett., p. 2167 Ul'Yanova, O.D., Pentin, Y.A., (1967) Russ. J. Phys. Chem., 41, p. 1447 Dionísio, M., Almeida, L.N., Moura-Ramos, J., (1990) Bull. Soc. Chim. Belg., 99, p. 215 Zefirov, N.S., Samoshin, V.V., Palyulin, V.A., (1983) Zh. Org. Khim., 19, p. 1888 Buys, H.R., De Vries, H.J.A., Hageman, H.J., Altona, C., (1970) Rec. Trav. Chim., 89, p. 245 Azandegbe, E.C., (1988) Thermochim. Acta, 130, p. 121 Cambie, R.C., Chambers, D., Rutledge, P.S., Woodgate, P.D., Woodgate, S.D., (1981) J. Chem. Soc., Perkin Trans., 1, p. 33 Rablen, P.R., Hoffmann, R.W., Hrovat, D.A., Borden, W.T., (1999) J. Chem. Soc., Perkin Trans., 2, p. 1719 Epiotis, N.D., (1973) J. Am. Chem. Soc., 95, p. 3087 Wiberg, K.B., Murcko, M.A., Laidig, K.E., MacDougall, P.J., (1990) J. Phys. Chem., 94, p. 6956 Wiberg, K.B., (1996) Acc. Chem. Res., 29, p. 229 Alabugin, I.V., Zeidan, T.A., (2002) J. Am. Chem. Soc., 124, p. 3175