Natural Product Biomolecules - Organic Chemistry Concepts: An EFL Approach - page 167

Turn the Fischer projection on its side as shown. This causes the ligands on the right
hand side to point below the proposed ring. The ligands from the left hand side point
above the proposed ring.
For D-series sugars, you must rotate the C 4 -C 5 bond as shown. This rotation places
the C 5 -OH in position for hemiacetal ring formation. As a result, the -CH 2 OH group
always points above the ring plane.
For L-series sugars, rotation in the opposite direction is needed. This rotation causes
the -CH 2 OH to point below the ring plane. Hemiacetal formation then gives the cyclic
structure.
Clearly the hemiacetal formation can have either configuration at the new chirality
center to give the α - (OH directed down) or β -anomer (OH directed up).
Try to draw these Haworth projections.
D You should have drawn the following:
Q 8.2. Draw the possible pyranose and furanose structures for d -fructose.
Q 8.3. Pick out any “reducing sugars” in Q 8.1 .
Q 8.4. How many isomers, including stereoisomers, are possible in a triglyceride
which is made from one unit each of palmitic, stearic, and oleic acids?
Q 8.5. The melting point of palmitoleic acid ( cis -9-hexadecenoic acid) is −1 °C.
This is very different from the melting point of palmitic acid which is
63 °C. Explain this.