The Major Functional Groups
1.
2.
3.
4.
5.
6.
7.
8.
Hydroxyls of alcohols
Carbonyls of aldehydes and ketones
Carboxyls of carboxylic acids
Aminos of amines
Sulfhydryls of thiols
Phosphates of organic phosphates
Methyl
Methylene
1. The Hydroxyl
 The hydroxyl group is an –O-H attached to
a hydrocarbon.
 Called alcohols
 Usually have “alcohol” or “ol” at the end
of the name.
 Example, the 2-carbon alcohol
◦ Called ethyl alcohol or ethanol
 Alcohols are the least oxidized (most
reduced) of all the oxygen-containing
functional groups.
Examples of Alcohols
• Isopropyl alcohol (rubbing alcohol)
– Note –OH is on middle carbon
– Soluble in water.
• Cholesterol
– Note –OH on lower left
– Insoluble in water.
• Glycerol
– Molecule with 3 –OH’s
– Soluble in water
Properties of Alcohols
• The hydroxyl group, -OH, is polar
– (See module 4 for polarity)
– Means it is hydrophilic or “water-loving”
• Alcohols smaller than 4 carbons are soluble in
water
– Example is 2-carbon alcohol, ethyl alcohol found
in alcoholic beverages.
• Alcohols larger than 4 carbons are insoluble in
water, such as cholesterol.
2. The Carbonyl Group
 The carbonyl is pronounced “car-bon-el”
 This is a double-bonded O attached to C
◦ =O
 At the end of a molecule called aldehyde
◦ CH3C=O called acetaldehyde
H
 In middle of molecule, called ketone
◦ CH3-C-CH3 called acetone (fingernail polish
O
remover)
The Carbonyl, continued
• The double-bonded oxygen without an H
means that it is less reduced (more oxidized)
• The carbonyl is more oxidized than the
hydroxyl but less than the carboxylic acid.
• Carbonyls CANNOT form hydrogen bonds with
itself because there is no H attached to the O.
Examples of Aldehydes
• Formaldehyde, a preservative
• Acetaldehyde,
a liver product
• Glucose, a combination
of aldehyde & alcohol
Examples of Ketones
• Carvone (caroway seeds)
(also used as fungicide)
• Thymine, a part of DNA
--has 2 ketones
3. The Carboxyl Group
 The carboxyl group is a carbon to which a
carbonyl AND a hydroxyl are added
or -COOH or –CO2H
 The most oxidized of all the functional groups.
 Can form hydrogen bonds.
 Molecules with a carboxyl group are called
carboxylic acids.
Carboxylic Acids
 The H from the carboxyl is easily donated so
carboxylic acids are acidic.
CH3COOH  CH3COO- + H+
acetic acid
acetate
hydrogen ion (proton)
 Carboxylic acids are the among the most
acidic of all the organic, or carbon-containing,
acids.
 Found frequently in living organisms.
Examples of Carboxylic Acids
• All amino acids, the subunits of proteins
alanine
• Some molecules of aerobic respiration,
because the carboxyl group can come off
as the waste gas CO2 which we exhale.
Pyruvic acid,
end of glycolysis
Citric Acid,
in Krebs cycle
has 3 carboxyls
4. The Amino Group
 A molecule containing a Nitrogen often as –
NH2
 May be located at the end or in the middle of
a molecule.
 Called amines.
The Amines
 Can accept a proton (H+) and so are basic or
alkaline.
CH3NH2 + H+  CH3NH3+
methyl amine proton methylammonium ion
 Can also form hydrogen bonds with other polar
groups.
◦ The hydrogen bonds holding DNA in the double helix
involve amines.
 Are often the decay products of proteins and so
smell terrible. 
Examples of Amines
• All amino acids have an amino group:
alanine
• Decay molecules such as putrescine
• Nucleotides such as thymine
5. Sulfhydryl Group
 Name is combination of “Sulfur” and “hydryl”
or “hydrogen-containing”.
 Have –S-H attached to the middle or end of a
molecule.
 Since sulfur is in the same family as oxygen, it
forms 2 covalent bonds.
 Called thiols.
An Example of Thiols
The most important thiol in living organisms is the
amino acid cysteine (cys)
The thiols of 2 cysteines can make a covalent bond,
the disulfide bridge, locking proteins into their
characteristic shape.
cys—CH2—S—S—CH2—cys
6. The Phosphate Group
 The phosphate group is a phosphorus atom with
4 oxygens attached.
 Two oxygens often donate their H’s, so
phosphate can carry a 2- charge, an anion, a
negatively-charged ion.
Examples of Phosphates
The Nucleic Acids all contain phosphates.
– ATP, the energy molecule, has 3 phosphates, one
of which may be used to transfer chemical energy
between molecules. (See module on energetics)
– DNA and RNA have backbones made of
phosphates alternating with a deoxyribose or
ribose monosaccharide.
– Molecules that accept Hydrogen such as NAD+ or
FAD+ contain phosphates.
Some important functional groups of organic
compounds
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
C
C
OH
)
STRUCTURE In a hydroxyl group (—OH), a
hydrogen atom is bonded to
an oxygen atom, which in turn
is bonded to the carbon
skeleton of the organic
molecule. (Do not confuse this
functional group with the
hydroxide ion, OH–.)
Figure 4.10
O
The carbonyl group
( CO) consists of a
carbon atom joined to an
oxygen atom by a double
bond.
When an oxygen atom is doublebonded to a carbon atom that is
also bonded to a hydroxyl group,
the entire assembly of atoms is
called a carboxyl group (—COOH).
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Some important functional groups of organic
compounds
NAME OF
COMPOUNDS
Alcohols (their specific
names usually end in -ol)
Ketones if the carbonyl group is
within a carbon skeleton
Carboxylic acids, or organic acids
Aldehydes if the carbonyl group is
at the end of the carbon skeleton
EXAMPLE
H
H
H
C
C
H
H
H
OH
H
C
H
C
H
present in alcoholic
beverages
H
C
H
Ethanol, the alcohol
H
O
H
Acetone, the simplest ketone
H
Figure 4.10
H
H
C
C
H
H
C
H
O
C
OH
Acetic acid, which gives vinegar its
sour tatste
O
C
H
Propanal, an aldehyde
21
• Some important functional groups of organic
compounds
AMINO
SULFHYDRYL
H
N
H
Figure 4.10
O
SH
(may be written HS
The amino group (—NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
PHOSPHATE
)
O
P
OH
OH
The sulfhydryl group consists of
a sulfur atom bonded to an
atom of hydrogen; resembles a
hydroxyl group in shape.
In a phosphate group, a phosphorus
atom is bonded to four oxygen atoms;
one oxygen is bonded to the carbon
skeleton; two oxygens carry negative
charges; abbreviated P . The
phosphate group (—OPO32–) is an
ionized form of a phosphoric acid
group (—OPO3H2; note the two
hydrogens).
22
7. Methyl Group
8. Methylene Group
9. Ester group
The ester functional group does
not look much different next to
the carboxylic acid functional
group. In fact you might notice
the only difference is the
hydrogen atom, present in the
carboxylic acid absent in the
ester. This IS the key difference.
Ester have carbon atoms in
place of that hydrogen.
• Esters have very pleasant odors.
Banana
Pineapple
Concept Check
1. Identify the 3 functional groups in this
molecule.
2. Which of the groups above form hydrogen
bonds?
3. Which of the groups above is basic?
Concept Check Answers
1.
amino
carboxyl
hydroxyl
2. All three functional groups will form
hydrogen bonds.
3. The amino group will accept a proton
and so is basic.