Section 22.3 Configurations of Aldoses 925
Movie:
Configurations of the
D-aldoses
Aldopentoses have three asymmetric carbons and therefore eight stereoisomers
(four pairs of enantiomers), while aldohexoses have four asymmetric carbons and 16
stereoisomers (eight pairs of enantiomers). The four D-aldopentoses and the eight
D-aldohexoses are shown in Table 22.1.
Diastereomers that differ in configuration at only one asymmetric carbon are called
epimers. For example,D-ribose and D-arabinose are C-2 epimers (they differ in con-
figuration only at C-2), and D-idose and D-talose are C-3 epimers.
HOH
HOH
HOH
CH 2 OH
HC O
C-2 epimers
HO H
HOH
HOH
CH 2 OH
O
HOH
H
HO H
HOH
CH 2 OH
HO
HC O HC O
C-3 epimers
HO H
HO H
HOH
CH 2 OH
HC HO H
D-ribose D-arabinose D-idose D-talose
CH 2 OH
HOH
HOH
HC O
CH 2 OH
HO H
HO H
HC O
CH 2 OH
HO H
HOH
HC O
CH 2 OH
H OH
H
HC O
HO
D-erythrose L-erythrose D-threose L-threose
TABLE 22.1 Configurations of the D-Aldoses
HC O
OH
CH 2 OH
H
OH
CH 2 OH
H
H OH
HC O
O
OH
CH 2 OH
H
H OH
H OH
HC O
OH
CH 2 OH
H
H OH
HO H
HC
OH
CH 2 OH
H
H OH
H OH
H OH
OH
CH 2 OH
H
H OH
H OH
HO H
HC O HC O
OH
CH 2 OH
H
H OH
HO H
H OH
OH
CH 2 OH
H
HO H
HC O
O
OH
CH 2 OH
H
HO H
H OH
HC O
OH
CH 2 OH
H
HO H
HO H
HC
OH
CH 2 OH
H
H OH
HO H
HO H
HC O HC O
OH
CH 2 OH
H
HO H
H OH
H OH
OH
CH 2 OH
H
HO H
H OH
HO H
HC O HC O
OH
CH 2 OH
H
HO H
HO H
H OH
OH
CH 2 OH
H
HO H
HO H
HO H
HC O HC O
D-glyceraldehyde
D-erythrose
D-ribose D-arabinose
D-allose D-altrose D-glucose D-mannose
D-threose
D-xylose D-lyxose
D-gulose D-idose D-galactose D-talose