Organic Chemistry

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