25.4. Organic Reactions http://www.ck12.org
CH 3 CHOHCH 3
Cr 2 O^27 −
?−→
H+CH 3 COCH 3
Tertiary alcohols cannot be oxidized in this way because the carbon to which the hydroxyl group is attached does
not have another hydrogen atom attached to it.
When a primary alcohol is oxidized to an aldehyde in the presence of water, the reaction can be difficult to stop
because the aldehyde can be further oxidized to the corresponding carboxylic acid. For example, the oxidation of
ethanal produces ethanoic (acetic) acid.
CH 3 CHO
Cr 2 O^27 −
?−→
H+CH 3 COOH
Ethanol-containing beverages such as wine are susceptible to such oxidation if kept for long periods of time after
having been opened and exposed to the air. Wine that has become oxidized will have an unpleasant vinegary taste
due to the production of acetic acid.
Unlike aldehydes, ketones are resistant to further oxidation because the carbonyl group is in the middle of the carbon
chain, so the ketone cannot be converted to a carboxylic acid.
Condensation Reactions
Acondensation reactionis a reaction in which two molecules combine to form a single molecule. A small molecule,
often water, is usually removed during a condensation reaction. Amino acids are important biological molecules that
have an amine functional group on one end of the molecule and a carboxylic acid functional group on the other end.
When two amino acids combine in a condensation reaction, a covalent bond forms between the amine nitrogen of
one amino acid and the carboxyl carbon of the second amino acid. A molecule of water is then removed as a second
product (Figure25.22).
FIGURE 25.22
Amino acids join together to form a
molecule called a dipeptide. The –OH
from the carboxyl group of one amino acid
combines with a hydrogen atom from the
amino group of the other amino acid to
produce water (blue).