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Chapter 4
Carbon and the
Molecular
Diversity of Life
1
• Carbon is the backbone
of biological molecules
(macromolecules)
• All living organisms are
made up of chemicals
based mostly on carbon
2
• Organic chemistry is the study of
carbon compounds
• Carbon atoms can form diverse
molecules by bonding to four other
atoms
• Carbon compounds range from
simple molecules to complex ones
• Carbon has four valence electrons
and may form single, double, triple,
or quadruple bonds
3
• The electron configuration
of carbon gives it covalent
compatibility with many
different elements
Nitrogen
Carbon
Hydrogen
Oxygen
(valence = 1)
(valence = 2)
(valence =
3)
(valence = 4)
H
O
N
C
Figure 4.4
4
Variations in Carbon Skeletons
5
The shapes of three simple organic molecules
6
• The bonding versatility of
carbon allows it to form many
diverse molecules, including
carbon skeletons
Name and
Comments
(a) Methane
Molecular Structural
Formula
Formula
Ball-andStick
Model
SpaceFilling
Model
H
CH4
H C
H
H
(b) Ethane
C2H
6
(c) Ethene
Figure 4.3 A-C (ethylene)
C2H4
H H
H C C H
H H
H
H
C C
H
H
7
• Hydrocarbons are molecules
consisting of only carbon and
hydrogen
• Hydrocarbons are found in many of a
cell’s organic molecules
Fat droplets (stained red)
Figure 4.6 A, B
(a) A fat molecule
100 µm
(b) Mammalian adipose cells
8
• Isomers are molecules with
the same molecular formula
but different structures and
properties (ex: glucose and
fructose)
• Three types of isomers are
–Structural
–Geometric
–Enantiomers
9
Three Types of Isomers
10
• Enantiomers are important in the
pharmaceutical industry
igure 4.8
L-Dopa
(effective
against
Parkinson’s
disease)
D-Dopa
(biologic
ally
inactive)
11
• Six functional groups are important in
the chemistry of life
–Hydroxyl
–Carbonyl
–Carboxyl
–Amino
–Phosphate
–Sulfhydryl
–ALL OF THE ABOVE ARE POLAR
AND HYDROPHILIC!
–Methyl (nonpolar and hydrophobic)
12
Functional Groups of Organic Compounds
pp. 64-65
13
• Functional
groups are the
parts of
molecules
involved in
chemical
reactions
• They give
organic
molecules
distinctive
chemical
properties
Figure 4.9
Estradiol
OH
CH3
HO
Female lion
OH
CH3
CH3
O
Testosterone
Male lion
14
Some important functional
groups of organic compounds
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
O
OH
(may be written HO
STRUCTURE
Figure 4.10
CARBOXYL
C
C
OH
)
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–.)
O
The carbonyl group
( CO) consists of a
carbon atom joined to
an oxygen atom by a
double bond.

When an oxygen atom is
double-bonded 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)
EXAMPLE
H
H
H
C
C
H
H
Ketones if the carbonyl group
is within a carbon skeleton
Aldehydes if the carbonyl
group is at the end of the
carbon skeleton
H
OH
Ethanol, the alcohol
present in alcoholic
beverages
H
H
C
H
C
H
H
Acetone, the simplest ketone
H
Figure 4.10
H
O
C
H
Carboxylic acids, or organic
acids
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
16
Some important functional groups of
organic compounds
AMINO
SULFHYDRYL
H
N
H
The amino group (—NH2)
consists of a nitrogen
atom bonded to two
hydrogen atoms and to
the carbon skeleton.
Figure 4.10
PHOSPHATE
O
SH
(may be written HS
)
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).
17