H. Booth, J. Dixon, Readshaw Simon
1992
Citations
0
Influential Citations
15
Citations
Journal
Tetrahedron
Abstract
Abstract The ΔH o a→e and ΔS o a→e values for conformational equilibria in 2-methoxytetrahydropyran have been determined by variable temperature nmr spectroscopy in solvents CD 2 Cl 2 , ether/CD 2 Cl 2 , ether/toluene and ether/methanol, whilst the corresponding values for conformational equilibria in 2-(2′,2′,2′-trifluoroethoxy)-tetrahydropyran have been determined in ether/toluene and ether/methanol. Replacement of toluene by methanol causes increases in ΔH o a→e and ΔS o a→e . These changes are consistent with a preferential hydrogen bonding of methanol to axial alkoxy groups, causing a decrease in both entropy and enthalpy of axial conformations relative to their equatorial counterparts. The enthalpy decrease is probably a result of an enhancement of the stabilising endo-anomeric effect.