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Chapter 11
Introduction to Organic Chemistry
Organic chemistry is the chemistry of the compounds of
carbon. The chemistry of carbon compounds is extremely
rich and complex and examples can be found all around
us. Gasoline, plastics, medicine, and textiles are but a few
examples. Perhaps the greatest example of the richness
and complexity of organic compounds comes in the form
of DNA. Because organic compounds are found in
everyday life, it is important to understand their structure
and behavior. What distinguishes one compound from
another? Why are some compounds toxic to living
organisms? Can we predict the reactivity of organic
compounds? It is these types of questions that are found
at the heart of Organic Chemistry.
Structural Formulae of Organic Compounds.
Because of the rich diversity of organic compounds, it is
important to show the proper connectivity of atoms when
drawing organic structures. For example, organic
chemists draw ethanol as:
H
H
H
C
C
H
H
O
H
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This structure is an expanded structure of ethanol and it
clearly shows the connectivity of all the atoms. The
problem with expanded structures is that with larger
molecules they can be cumbersome to draw and difficult
to read. Because of this, chemists have developed
different methods to represent molecules.
In a condensed structure, hydrogen atoms are grouped
with the atom that they are attached to. Therefore, the
condensed structure of ethanol would look like:
CH3CH2OH
In a line-bond structure, hydrogen atoms attached to
carbon are omitted and carbon-carbon bonds are
represented as lines. In a line bond structure, carbon
atoms are located at the ends of the lines and the vertices
where the lines meet. The line bond structure for ethanol
is:
OH
Important: If you draw a ‘c’, you must draw all the
atoms attached to it.
H
H
H
H
H
C
C
C
C
H
H
H
H
H
or
CH3CH2CH2CH3
but not
C
C
C
or
C
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e.g. Complete the following table.
Expanded
Condensed
Line-Bond
Formula
H
C
H
C
C
H
H
C
C
C
H
H
CH3CH2OCH3
O
Organic Compounds.
Since organic compounds primarily consist of carbon,
hydrogen, oxygen, nitrogen, sulfur, and the halogens, it is
important that you understand the types and number of
bonds that these elements form. Recall in Chapter 4 that
carbon has four valence electrons which it can share to
form four covalent bonds. Hydrogen and the halogens
only form one covalent bond. In either case they acquire
a noble gas configuration (helium through to xenon).
Nitrogen forms three covalent bonds and oxygen and
sulfur typically form two covalent bonds. Shown below
are some typical examples. It is important that you
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become familiar with the number of covalent bonds most
often formed by these elements.
H
C
Cl
H
C
O
N
H
Cl
C
H
H
H
O
O
N
H
H
H
Cl
S
Cl
S
C
H
S
Functional Groups.
The amount of organic compounds found in nature
number in the millions and more are synthesized each
day. Fortunately, this vast number of organic compounds
can be organized via characteristic structural features
called functional groups. Functional groups are certain
groups of atoms that undergo similar reactions. The
functional groups also allow us to systematically name
each organic molecule according to their family.
Functional groups can be broken down into three main
categories.
1. Functional groups with carbon in multiple bonds.
• alkenes (contains C=C)
• alkynes (contains C≡C)
• aromatic (has alternating C-C and C=C bonds in a six
atom ring)
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2. Functional groups with heteroatoms (atoms other than
carbon or hydrogen) in single bonds.
• haloalkane (contains C-X, where X = F, Cl, Br, or I)
• ether (contains C-O-C)
• amine (contains C-N)
• alcohol (contains C-O-H)
• phenol (contains C-O-H where C is part of an
H
aromatic ring)
O
• thiol (contains C-S-H)
3. Functional groups with heteroatoms in multiple bonds.
• ketone (contains C=O with two C attached)
• aldehyde (contains C=O with H attached)
• carboxylic acid (contains C=O with OH attached)
• ester (contains C=O with O-C attached)
• amide ( contains C=O with N attached)
Because C=O appears in so many functional groups it has
a special name. It is called a carbonyl group. A carbonyl
group itself is not a functional group but is part of many
functional groups.
Although Timberlake considers alkanes as a functional
group, we will not. Consider alkanes as molecules
without functional groups.
It is important that you become familiar with these
functional groups. You must know the following Table.
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Family
Functional Group
Alkene
Alkyne
C
C
C
C
carbon-carbon double bond
carbon-carbon triple bond
six carbon atom ring with
alternating single and double
bonds
C
C
Aromatic
C
C
C
C
Haloalkane
Ether
X
carbon-halogen bond. X = F,
Cl, Br, I
OH
carbon bonded to a hydroxyl
group (OH)
C
Alcohol
C
C
Thiol
C
oxygen atom bonded between
two carbon atoms
SH
carbon bonded to a –SH group
O
C
O
Aldehyde
Characteristic
C
H
carbonyl group (C=O) bonded
to a hydrogen atom
O
Ketone
C
C
C
O
Carboxylic Acid
C
OH
carbonyl group bonded to two
carbon atoms
carbonyl group bonded to a
hydroxyl group
O
Ester
Amine
C
O
C
C
N
O
Amide
C
N
carbonyl group bonded to an
oxygen atom
carbon atom bonded to a
nitrogen atom
carbonyl group bonded to a
nitrogen atom
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Identify the functional group(s) in the following
molecules:
OH
CH3CH2O
O
C
H3C
CH3
ethyl acetate
O
C
OH
OCH3
acetic acid
H
C
H
O
O
C
H
formaldehyde
vanillin
O
C
CH3
O2 N
NO2
HO
CH2CH3
N
CH2CH3
O
NMe
CH3
NO2
trinitrotoluene
H
HO
insect repellant
morphine
H3C CH3
CH3
H3C
CH3
CH3
CH3
CH3
H3C CH3
β-carotene
Cl
H
C
CCl3
Cl
O
Cl
Cl
O
Cl
Cl
dichloro-diphenyl-trichloroethane (DDT)
2,3,7,8-tetrachlorodibenzodioxin (dioxin)
CH3 OH
C CH
O
CH3O
O
N
H
HO
norethindrone
capsaicin
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As an example of the complexity of molecules that can be
synthesized, consider Brevetoxin B below. Twelve years
in the making, Brevetoxin B required 83 individual
reactions in order to be synthesized.
O
H
OH
Me
H O
Me
O
O
H
H
O
Me
H
H
O
H
O
Me
O
H H
Me
H
O
H
H O
Me
H
O
O
H
O H
H
Me
brevetoxin B
It should be evident by the many different functional
groups that the structure of the molecule is very
important. Consider the molecules of ethyl alcohol and
dimethyl ether. Although they have the same molecular
formula, their molecular structure is clearly different.
Note their different physical and chemical properties.
CH3
molecular formula
molar mass
room temperature
melting point
boiling point
reaction with Na
CH2
OH
C2H6O
46 g/mol
liquid
-117 °C
78 °C
vigorous
CH3
O
CH3
C2H6O
46 g/mol
gas
-138 °C
-25 °C
none
You will see that many molecules can have the same
molecular formula but different arrangement of atoms.
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This property is called isomerism. Molecules with
identical molecular formulas but different connectivity of
atoms are called constitutional isomers. Therefore, the
two molecules shown above, ethyl alcohol and dimethyl
ether are constitutional isomers.
e.g. Indicate whether each of the following pairs of
molecules represents identical compounds, constitutional
isomers, or different compounds that are not
constitutional isomers.
a.
b.
CH3
CH3
CH3
CH2
CH
O
CH2
CH2
CH3
CH3
CH3
CH3
CH3
CH
CH
CH3
CH2
CH
CH2
CH3
O
O
c.
CH3
CH2
C
H
CH2
OH
d.
Draw all the constitutional isomers for C5H12.
CH3
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How many constitutional isomers can you draw for
C4H8O?
Reactions of Organic Compounds.
Approximately 90% of all organic reactions can be
classified into three categories:
1. Addition Reactions. Molecules containing multiple
bonds tend to undergo addition reactions. These include
alkenes, alkynes, and molecules containing a carbonyl
group.
2. Elimination Reactions. Molecules containing single
bonds to heteroatoms tend to undergo elimination
reactions. Elimination reactions are essentially the
reverse of addition reactions.
3. Substitution Reactions. In substitution reactions,
one atom/group on a molecule is replaced (substituted) by
another atom/group. Most of the substitution reactions
will see will involve alkanes and aromatic molecules.
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Important Concepts from Chapter 11
• Structures of Organic Compounds
Expanded
Condensed
Line-Bond
• Isomers
Constitutional Isomers
• Organic Reactions
• Functional Groups!
Addition Reactions
Elimination Reactions
Substitution Reactions