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Solutions for Carbohydrates and Nucleic Acids
65 continued
X:
CH2OH
H OH
HO H
CHO
HO H
CH2OH
H OH
HO H
CHO
H OH
HO H
HHO
CHO
HHO
OHH
CH2OH
HNO3
HNO3
HHO
CHO
OHH
CH2OH
HHO
OHH
COOH
HHO
OHH
COOH
COOH
H OH
HO H
COOH
HO H
HNO3
COOH
H OH
COOH
HO H
The other aldohexose that gives an optically inactive aldaric acid is D-allose, with all OH groups on the 
right side of the Fischer projection. Ruff degradation followed by nitric acid gives an optically inactive 
aldaric acid, however, so X cannot be D-allose.
(c) X is D-galactose.
Ruff
optically inactive
optically active
(d) The optically active, five-carbon aldaric acid comes from the optically active pentose, not from the 
optically inactive, six-carbon aldaric acid. The principle is not violated.
(e)
Ruff
D-threose (S,S)-tartaric acid
optically active
CH2OH
H OH
HO H
C
CH2OH
O
HO H
CH2OH
H
HO
OH
HO O
OH
H
H
66 Tagatose is a monosaccharide, a ketohexose, that is found in the pyranose form.
(a) (b)
1
2
34
5 6
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