Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)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.78515991605Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)