Mutarotation in alpha-glucose

[dttom]

In this case there are more beta form (~64%) than alpha form (~36%), yet through anomeric effect the alpha form should be preferred with its anomeric hydroxyl group in axial conformation. So is this a counterargument or there are some other reasons?

[Horza2002]

Your right, when considering the electronic effect of the anomeric effect should have the hydroxyl group in the axial position. But you also have to consider the steric effects. If you look up chair conformations it should explain that groups are more stable in the equatorial poistion.

 

With the hydroxyl group in the axila position, it essentially bangs into the group that are on the 3 and 5 carbons and so disfavours the axial position.

 

The observed ratio of isomers results from the compraimse between these two effects

[dttom]

I see, that means the ratio represents a coupling of the effects.

[Horza2002]

yer thats right. Its just the two affects competeing against each other and that ratio is the result