Ring Structure for Fructose:
The chair form of fructose follows a similar pattern as that
for glucose with a few exceptions. Since fructose has a ketone
functional group, the ring closure occurs at carbon # 2. See
the graphic on the left.
In the case of fructose a five membered ring is formed. The
-OH on carbon #5 is converted into the ether linkage to close
the ring with carbon #2. This makes a 5 member ring - four carbons
and one oxygen.
Steps in the ring closure (hemiketal synthesis):
1. The electrons on the alcohol oxygen are used to bond the carbon
#2 to make an ether (red oxygen atom).
2. The hydrogen (green) is transferred to the carbonyl oxygen
(green) to make a new alcohol group (green).
The ring structure is written with the orientation depicted
on the left for the monosaccharide and is consistent with the
way the glucose is depicted.
Hemiketal Functional Group:
The anomeric carbon is the center of a hemiketal functional
group. A carbon that has both an ether oxygen and an alcohol
group (and is attached to two other carbons is a hemiketal.
graphic of hemiacetal/hemiketal in a new window
Which carbon in the structure on the left is the anomeric
Then check the answer from the drop down menu.