Untitled - Kelly Walsh High School

Organic, Biochemistry, and Polymers 319
Be Careful!
A condensation reaction joins two molecules and splits out a small molecule. The
small molecule is usually water. The formation of a peptide bond is an example
of a condensation reaction. The conditions necessary for a condensation reaction
vary with the functional groups involved. In most cases, a catalyst will be present.
The two most common catalysts are acids and enzymes. Two alcohols will condense
to form an ether. A carboxylic acid condenses with an alcohol to form an
ester. A carboxylic acid condenses with an amine to form an amide.
A carboxylic acid can react with an amine via an acid-base reaction. Take care to
bypass this reaction.
The following illustrates the reaction of two alcohols to form an ether. The
reacting molecules are both molecules of a-glucose. This reaction occurs in the
presence of an enzyme catalyst, which prevents the other functional groups
from reacting. In biochemistry, an ether group is a glycoside linkage. The joining
of two molecules of the monosaccharide, b-glucose, gives the disaccharide,
lactose. The joining of additional b-glucose molecules will eventually generate
the polysaccharide, cellulose. If we replace the b-glucose with a-glucose, the
disaccharide would be maltose. A polysaccharide of a-glucose is starch.
H
C
HO
HO
OH
CH 2
C
H
H
C
HO
HO
C
H
OH
CH 2
C
H
H
C
C
H
O
C
OH
H
C
H
O
C
OH
H
OH
H
C
HO
HO
OH
CH 2
C
H
H2O removed
H
C
O
HO
OH
CH 2
C
H
C
H
C
H
H
C
H
C
O
O
C
OH
C
OH
H
H
OH
OH