text: A widely accepted explanation is that there is a stabilizing interaction (hyperconjugation) between the unshared electron pair on the endocyclic heteroatom (within the sugar ring) and the σ* orbital of the axial (exocyclic) C–X bond. This causes the molecule to align the donating lone pair of electrons antiperiplanar (180°) to the exocyclic C-X σ bond, lowering the overall energy of the system and causing more stability.
  Some authors also question the validity of this hyperconjugation model based on results from the quantum theory of atoms in molecules. While most studies on the anomeric effects have been theoretical in nature, the n–σ* (hyperconjugation) hypothesis has also been extensively criticized on the basis that the electron density redistribution in acetals proposed by this hypothesis is not congruent with the known experimental chemistry of acetals and, in particular, the chemistry of monosaccharides.