Chemistry Reference
In-Depth Information
16.23
H
O
H
H
O
OH
H
H
H
H
OH
OH
OH
H
OH
OH
OH
OH
α
-pyranose
β
-pyranose
H
OH
2
C
H
H
OH
2
C
OH
H
H
H
H
O
O
H
OH
H
H
OH OH
α
-furanose
OH
OH
β
-furanose
16.24
One way of approaching this problem is to relate the structure to something familiar,
for example the structure of glucose. Inspection of the ball-and-stick structure
reveals that it represents a
β
-hexopyranose (6 carbons; 6-membered ring with an OH
group bonded to the anomeric carbon). Recall that
β
-D-glucopyranose has all of the
six-membered ring substituents on equatorial sites (see Secs. 16.7 and 16.11). The
ball-and-stick structure has all substituents equatorial with the exception of the C-3
hydroxyl group, which is axial. Thus, this structure is the C-3 epimer of
β
-D-
glucopyranose. Inspection of Table 16.1 reveals that D-allose is the C-3 epimer of D-
glucose. Thus, the structure represents
β
-D-allopyranose. The Fischer, Haworth and
line-segment structures of this compound are shown below. Notice that the line
segment structure most closely resembles the ball-and-stick structure.
H
OH
HOH
2
C
OH
H
H
OH
H
OH
H
O
O
O
H
OH
H
H
HO
H
OH
H
OH
HO
H
HO
OH
H
H
OH
OH
CH
2
OH
16.25
Consult the answer to Problem 16.7.
OH
H
H
O
H
H
β
H
-D-threofuranose
