Chapter 25: Carbohydrates

Mutarotation : interconversion of a- and b- anomers

• The a- and b- anomers of carbohydrates are typically stable solids.
• However, in aqueous solution, they quickly equilibrate to an equilibrium mixture of the two forms.
• For example, in aqueous solution, glucose exists as a mixture of 36% a- and 64% b- (>99% of the pyranose forms exist in solution).
• The equilibration occurs via the ring opening of the cyclic sugar at the anomeric center with the acyclic form as the intermediate.

• Or, in a simplified form with all the "extra" hydroxy groups removed:

• The curly arrow mechanism involved here is essentially the same as that for acetal formation (review ?)