Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/80232
Type: Artigo de periódico
Title: Influence of OH center dot center dot center dot N and NH center dot center dot center dot O inter- and intramolecular hydrogen bonds in the conformational equilibrium of some 1,3-disubstituted cyclohexanes through NMR spectroscopy and theoretical calculations
Author: de Oliveira, PR
Viesser, RV
Guerrero, PG
Rittner, R
Abstract: The analysis of concentration effects in the (1)H NMR data of cis-3-aminocyclohexanol (ACOL) showed that its diequatorial conformer changes from 60%at 0.01 mol L(-1) to 70% at 0.40 mol L(-1) in acetone-d(6). A similar increase was also observed for the diequatorial conformer of cis-3-N-methylaminocyclohexanol (MCOL), from 32% (CDCl(3) 0.01 mol L(-1)) to 55% (CDCl(3) 0.40 mol L(-1)). The increase in solvent basicity leads to a large stabilization effect for the diequatorial conformer of both compounds too. For ACOL, it changes from 47% (Delta G(egeq-axax) = 0.06 kcal mol(-1)) in CCl(4) to 93% (Delta G(eqeq-axax) = -1.53 kcal mol(-1)) in DMSO, while for MCOL it goes from 7% (Delta G(egeq-axax) = 1.54 kcal mol(-1)) in CCl(4) to 82% (Delta G(egeq-axax) = -0.88 kcal mol(-1)) in pyridine-d(6). These results indicate that the intramolecular hydrogen bonds (IAHB) OH center dot center dot center dot N and NH center dot center dot center dot O stabilize the diaxial conformers of these compounds in a non-polar solvent. For cis-3-amino-1 -methoxycyclohexane (ACNE) and cis-3-N-methylamino-1-methoxy-cyclohexane (MCNE) no changes were observed in equilibrium with the variation of solvent polarity. These results indicate for the first time that the IAHB NH center dot center dot center dot O is not strong enough to stabilize the diaxial conformer of these compounds and that the conformation equilibria of the cis isomers of compounds ACOL and MCOL are influenced only by the IAHB OH center dot center dot center dot N. Moreover, the presence of a secondary amino group (93% of diaxial conformer in CCl(4)) leads to an IAHB OH center dot center dot center dot N stronger than in primary and tertiary amino-derivatives (53 and 54% of diaxial conformer, respectively) for 1,3-disubstituted cyclohexanes. Values obtained from the theoretical data through the B3LYP functional are in agreement with the experimental results and indicate that the IAHB strength that influences the conformational equilibrium of these compounds is the IAHB OH center dot center dot center dot N. Thus, the IAHB NH center dot center dot center dot O do not stabilize the diaxial conformer of the cis isomer of compounds ACNE and MCNE showing that the diequatonal conformer will always be more stable than the diaxial conformer, independent of concentration or solvent. (C) 2011 Elsevier B.V. All rights reserved.
Subject: Conformational analysis
NMR spectroscopy
Theoretical calculations
Intramolecular hydrogen bond
Aminocyclohexanols
Country: Inglaterra
Editor: Pergamon-elsevier Science Ltd
Rights: fechado
Identifier DOI: 10.1016/j.saa.2011.02.010
Date Issue: 2011
Appears in Collections:Unicamp - Artigos e Outros Documentos

Files in This Item:
File Description SizeFormat 
WOS000289864300039.pdf236.38 kBAdobe PDFView/Open


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.