Mutarotational Equilibrium - Alpha vs Beta

[gettheleadout]

TBR and the wikipedia page for mutarotation state that beta-D-glucopyranose predominates over alpha-D-glucopyranose, with the ratio sitting at about 64% beta to 36% alpha.

However, this seems to stand in stark contrast to the anomeric effect, which suggests that the alpha configuration should predominate.

So what's the truth?

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[PlumbLine]

I think it goes back to axial substituents causing steric strain, leading to equatorial being favored. In the case of carbs, that strain is partially offset by the anomeric effect, which causes there to be a higher percentage of alpha than one would expect. I see what you mean though, in your link it says that alpha predominates, so that's confusing. In my Kaplan review book it gives glucose as an example of mutarotation, and says that Beta is favored 64% of the time.

 

[gettheleadout]

Yeah see I get the steric issue, but by definition the anomeric effect states that alpha predominates, so it would imply that whatever stereoelectronic effects are present outweigh the steric interactions.