The anomers of glucopyranose are diastereomers, with the " beta " anomer having an OH group pointing up equatorially, and the " alpha " anomer having that OH group pointing down axially.
12.
This classical approach typically requires multiple protection / deprotection steps in addition to the key anomeric activation / coupling reaction which, depending upon the glycosyl donor / acceptor pair, can lead to a mixture of anomers.
13.
Therefore, one can use a polarimeter to measure the rotation of a sample and then calculate the ratio of the two anomers present from the enantiomeric excess, as long as one knows the rotation of each pure anomer.
