Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/93597
Type: Artigo de periódico
Title: Conformational Analysis And Stereoelectronic Effects In Trans-1,2-dihalocyclohexanes: 1h Nmr And Theoretical Investigation
Author: Freitas M.P.
Rittner R.
Tormena C.F.
Abraham R.J.
Abstract: 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.
Editor: 
Rights: fechado
Identifier DOI: 10.1016/j.saa.2004.07.007
Address: http://www.scopus.com/inward/record.url?eid=2-s2.0-17844410384&partnerID=40&md5=1135dbe03b9671dd7d577e44f2bfe1da
Date Issue: 2005
Appears in Collections:Unicamp - Artigos e Outros Documentos

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