The relevant effect of an intramolecular hydrogen bond on the conformational equilibrium of cis-3-methoxycyclohexanol compared to trans-3-methoxycyclohexanol and cis-1,3-dimethoxycyclohexane

H-1 NMR data show that an increase in the concentration of cis-3-methoxycyclohexanol (cis-3-MCH) shifts the conformational equilibrium from the 1aa conformer, stabilized by an intramolecular hydrogen bond (IAHB), to the fee conformer [X-ee = 44% (at 0.05 mol L-1) to 59% (at 0.40 mol L-1), in CCl4], which forms intermolecular hydrogen bonds (IEHB), as confirmed by IR data. The percentage of lee conformer increases with the solvent polarity, from 33% (Delta G(ee-aa) = 1.72 kJ mol(-1)) in cyclohexane (C6D12) to 97% (Delta G(ee-aa) = -8.41 kJ mol(-1)) in DMSO. For trans-3-methoxycyclohexanol (trans-3-MCH), lae and lea conformers are almost equally present in the studied solvents, lae increasing from 41%, in C6D12 (Delta G(ae-ea) = 0.84 kJ mol(-1)), to 49%, in DMSO (Delta G(ae-ea), = 0.13 kJ mol-1). A value of 18.4 kJ mol(-1) for the strength of IAHB in cis-3-MCH was obtained, from the theoretical data, through the CBS-4M method. (c) 2004 Elsevier B.V. All rights reserved.