text: An extension of the anomeric effect, the exo anomeric effect is the preference of substituents coming off a ring to adopt the gauche conformation, while sterics would suggest an antiperiplanar conformation would be preferred.  
  An example of this is 2-methoxytetrahydropyran.  As the anomeric effect predicts, the methoxy substituent shows an increased preference for the axial conformation. However, there is actually more than one possible axial conformation due to rotation about the C-O bond between the methoxy substituent and the ring.  When one applies the principles of the reverse anomeric effect, it can be predicted that the gauche conformer is preferred, suggesting the top left conformation is best in the figure above. This prediction is supported by experimental evidence.  Furthermore, this preference for the gauche position is still seen in the equatorial conformation.