Chemistry Reference
In-Depth Information
Monosaccharides react with alcohols (H
+
catalyst) to give
glycosides.
The -OH
group at the anomeric carbon is replaced by an -OR group. The product is an acetal.
Alcohols and phenols often occur in nature combined with sugars as glycosides, which
renders them water-soluble.
Disaccharides
consist of two monosaccharides linked by a glycosidic bond between
the anomeric carbon of one unit and a hydroxyl group (often on C-4) of the other unit.
Examples include
maltose
and
cellobiose
(formed from two glucose units joined by a
1,4-linkage and differing only in configuration at the anomeric carbon, being
α
and
β
,
respectively),
lactose
(from a galactose and glucose unit linked 1,4 and
β
), and
sucrose,
or
cane sugar (from a fructose and glucose unit, linked at the anomeric carbon of each, or 1,2).
Sugars such as fructose, glucose, and sucrose are sweet, but others (for example, lactose
and galactose) are not. Some noncarbohydrates, such as
saccharin
and
aspartame,
also
taste sweet.
Polysaccharides
have many monosaccharide units linked by glycosidic bonds.
Starch
and
glycogen
are polymers of
D
-glucose, mainly linked 1,4 or 1,6 and
α
.
Cellulose
consists of
D
-glucose units linked 1,4 and
β
.
Monosaccharides with modified structures are often biologically important. Examples
include
sugar phosphates, deoxy sugars, amino sugars,
and
ascorbic acid
(vitamin C).
Reaction Summary
Hydrolysis
H
3
O
+
H
3
O
+
polysaccharide
oligosaccharide
monosaccharide
Acyclic and Cyclic Equilibration
HO
CH
2
HO
CH
2
anomeric carbon
CH
OH
CH
O
HO
CH
CH
O
HO
CH
CH
OH
CH
CH
CH
CH
H
OH
H
OH
acyclic (aldehyde)
cyclic (hemiacetal)
