Anomeric effect aldopyranosides

Computation of the conformational energies of 2-methoxytetrahydropyran, a model for the methyl aldopyranosides, gave results in agreement with experimental observations. A preference for the axial conformer was apparent, but the nature of the stabilizing factor (anomeric effect) was not resolved. Force-field calculations have been extended to include alcohols, ethers, simple acetals, and 2-methoxytetrahydropyran. 2 The preference of 2-methoxytetrahydropyran for the axial conformer was attributed to interaction of the axial lone-pair orbital on the ring-oxygen atom with the axial C—O bond of the methoxy-group, which can be represented by the resonance structure (501) (see also, Vol. 6, p. 163). 

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