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

Spectrochim Acta A Mol Biomol Spectrosc. 2005 Jun;61(8):1737-45. doi: 10.1016/j.saa.2004.07.004.

Abstract

1H 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 1ee conformer [X(ee) = 44% (at 0.05 molL(-1)) to 59% (at 0.40 molL(-1)), in CCl4], which forms intermolecular hydrogen bonds (IEHB), as confirmed by IR data. The percentage of 1ee conformer increases with the solvent polarity, from 33% (DeltaG(ee-aa) = 1.72 kJmol(-1)) in cyclohexane (C6D12) to 97% (DeltaG(ee-aa) = -8.41 kJmol(-1)) in DMSO. For trans-3-methoxycyclohexanol (trans-3-MCH), 1ae and 1ea conformers are almost equally present in the studied solvents, 1ae increasing from 41%, in C6D12 (DeltaG(ae-ea) = 0.84 kJmol(-1)), to 49%, in DMSO (DeltaG(ae-ea) = 0.13 kJmol(-1)). A value of 18.4 kJmol(-1) for the strength of IAHB in cis-3-MCH was obtained, from the theoretical data, through the CBS-4M method.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cyclohexanes / chemistry
  • Cyclohexanols / chemistry*
  • Cyclohexylamines / chemistry*
  • Hot Temperature
  • Hydrogen / chemistry
  • Hydrogen Bonding
  • Magnetic Resonance Spectroscopy
  • Models, Chemical
  • Molecular Conformation
  • Molecular Structure
  • Peptides, Cyclic
  • Solvents
  • Spectrophotometry
  • Thermodynamics

Substances

  • Cyclohexanes
  • Cyclohexanols
  • Cyclohexylamines
  • Peptides, Cyclic
  • Solvents
  • cis-1,3-dimethoxycyclohexane
  • cis-3-methoxycyclohexanol
  • Hydrogen