Anomenc effect

This series of experiments establishes that % (Fig. 2) is the most stable spiroketal conformation it also demonstrates the importance of two electronic effects in the same function. The value of 1.4 kcal/mol for an anomenc effect must, however, be considered as a minimum value, because similar conclusions would have been reached with a value as high as 1.7 kcal/mol. 

Section 23.9 Pyranose forms of carbohydrates resemble cyclohexane in their conformational preference for chair forms. The anomenc effect causes an electronegative substituent at the anomeric (C-1) carbon to be more stable when it is axial than when it is equatorial. The effect is believed to result from the delocalization of an electron pair of the ring oxygen into an antibonding orbital of the anomeric substituent. 

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