Question

oup e i ent i S caPapie to act as n veducin s enown 6. Draw the ring structures for (-D-fructose and for e-bsfructoseS 7. An unknown carbohydrate gave a red precipitate when tested with Fehling's reagent, turned red when reacted with Seliwanoff's reagent, and quickly gave a red precipitate when reacted with Barfoed's reagent. What conclusions can be made about this carbohydrate? 9. What test could be used to differentiate between sucrose and lactose? Explain.

Answer 1

Ring structure of fructose is five a membered ring. It is formed when OH of carbon-5 of fructose (fisher projection) reacts with carbon -2.

There are two possibilities for ring structure of fructose alpha and beta fructose

Beta position -the -OH being on the same side of the ring as the C -6. In the ring structure this results in an upwards projection for the -OH on carbon 2.

Alpha position -the -OH being on the opposite side of the ring as the C - 6. In the ring structure this results in a downward projection for the -OH on carbon - 2.

6CH2OH CH2OH CH2OH OH 3 OH 3 CH2OH OH OH alpha-D-fructose Beta-D-fructose