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|Type:||Artigo de periódico|
|Title:||Conformational Analysis Of Trans-2-halocyclohexanols And Their Methyl Ethers: A 1h Nmr, Theoretical And Solvation Approach|
|Abstract:||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.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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