Chapter 10 Introduction to Organic
Chemistry: Alkanes
Organic Chemistry
An organic compound
10.1
Organic Compounds
•
•
•
•
is a compound made from carbon atoms.
has one or more C atoms.
has many H atoms.
may also contain O, S, N, and halogens.
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1
Organic Compounds
2
Organic vs. Inorganic
Typical organic compounds
• Propane, C3H8, is an
organic compound used
as a fuel.
•
•
•
•
•
have covalent bonds.
have low melting points.
have low boiling points.
are flammable.
are soluble in nonpolar
solvents.
• are not soluble in water.
• NaCl, salt, is an
inorganic compound
composed of Na+ and
Cl− ions.
Why is propane organic,
but NaCl is not?
oil (organic) and water (inorganic)
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Copyright © 2009 by Pearson Education, Inc.
3
Comparing Organic and Inorganic
Compounds
4
Learning Check
Identify each characteristic as most typical of compounds
that are 1) inorganic or 2) organic.
A.
B.
C.
D.
E.
F.
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5
has a high melting point.
is not soluble in water.
has a formula CH3─CH2─CH3.
has a formula MgCl2.
burns easily in air.
has covalent bonds.
6
Solution
Writing Formulas for Alkanes
In organic compounds,
• carbon has 4 valence electrons and hydrogen has 1.
Identify each characteristic as most typical of compounds
that are 1) inorganic or 2) organic.
1
2
2
1
2
2
A.
B.
C.
D.
E.
F.
•
•C•
•
has a high melting point.
is not soluble in water.
has a formula CH3─CH2─CH3.
has a formula MgCl2.
burns easily in air.
has covalent bonds.
H•
• carbon achieves an octet by forming four bonds.
H
H
••
H:C:H
H
••
H
C
H
H
CH4, methane
7
Tetrahedral Structure of Carbon
8
Organic Molecules
In organic molecules,
• valence electrons are shared.
• covalent bonds form between carbon atoms.
VSEPR theory
predicts that a
carbon atom with
four single,
covalent bonds has
a tetrahedral
shape.
H
••
H
••
H:C:C:H
••
H
••
H
H
H
H
C
C
H
H
H
Ethane, CH3─CH3
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10
Chapter 10 Introduction to Organic
Chemistry: Alkanes
Tetrahedral Structure of Carbon
10.2
Alkanes
In molecules with
two or more carbon
atoms, each
carbon atom with
four single bonds
has a tetrahedral
shape.
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12
Expanded and Condensed
Structures
Structural Formulas
Alkanes are written with structural formulas that are
• expanded to show each bond.
• condensed to show each carbon atom and its
attached hydrogen atoms.
Expanded
H
H
C
Condensed
H
CH4 , methane
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H
13
Structural Formulas
Names of Alkanes
The names of alkanes
• are determined by the IUPAC (International Union of
Pure and Applied Chemistry) system.
• end in –ane.
• with 1-4 carbons in a chain use prefixes as follows:
Condensed formulas are written for expanded
structural formula by showing each carbon and the
attached hydrogen atoms.
Expanded
Condensed
H H H H
│ │ │ │
H─C ─C ─C ─C ─ H
│ │ │ │
H H H H
14
Name
CH3─CH2─CH2─CH3
# Carbons
Condensed Structural
Formula
CH4
1
Methane
Ethane
2
CH3―CH3
Propane
3
CH3―CH2―CH3
Butane
4
CH3―CH2―CH2―CH3
15
Names of Alkanes
16
Learning Check
Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.
# Carbons
Structural Formula
Name
Pentane
5
Hexane
6
CH3CH2CH2CH2CH2CH3
Heptane
7
CH3CH2CH2CH2CH2CH2CH3
Octane
8
CH3CH2CH2CH2CH2CH2CH2CH3
Nonane
9
CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane
10
A. Write the condensed formula for:
H H
H
H
H
CH3CH2CH2CH2CH3
H
C
C
C
C
C
H
H
H
H
H
H
B. What is its molecular formula?
C. What is its name?
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
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18
Solution
Writing Structural Formulas
A. CH3─CH2─CH2─CH2─CH3
Carbon atoms in a chain
B. C5H12
•
•
•
•
C. pentane
maintain tetrahedral shape.
are connected in a zigzag pattern.
are drawn as 2-dimensional.
can be written in several conformations.
19
Some Structures for Butane
20
Hexane Has Six Carbon Atoms
Hexane
• is an alkane with six carbon atoms in a continuous
chain.
• has a “zigzag” look because each carbon atom is at
the center of a tetrahedron.
• is represented by a ball-and-stick model as shown
below.
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21
Learning Check
22
Solution
Write the condensed structural formula for
Write the condensed structural formula for
A. ethane.
A. ethane
B. heptane.
B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3
23
CH3─CH3
24
Cycloalkanes
Cycloalkanes
The structural formulas of cycloalkanes are usually
represented by geometric figures.
Cycloalkanes
• are cyclic alkanes.
• have two hydrogen atoms fewer than the open
chain.
• are named by using the prefix cyclo- before the
name of the alkane chain with the same number of
carbon atoms.
25
More Cycloalkanes
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26
Learning Check
Name the following.
A. CH3─CH2─CH2─CH3
B.
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3
D.
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Chapter 10 Introduction to Organic
Chemistry: Alkanes
Solution
Name the following:
A. CH3─CH2─CH2─CH3
B.
28
10.3
Alkanes with Substituents
butane
cyclopropane
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 octane
D.
cyclohexane
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30
Isomers of Butane
Alkyl groups
Alkyl groups are
• alkanes that are missing one H.
• substituents attached to carbon chains.
• named with a –yl ending.
Isomers
• have the same
molecular formula.
• have different atom
arrangements.
• of butane (C4H10) are a
straight chain and a
branched chain.
CH3
CH3
methyl
CH2
ethyl
31
Naming Substituents
32
Guide to Naming Alkanes
In the IUPAC system,
• a carbon branch is
named as an alkyl
group.
• halogen atoms are
named as halo.
33
Alkanes with Substituents
34
Naming Alkanes
Give the name of
CH3
CH3 CH
methylpropane
CH3
STEP 1:
CH3 CH3
⎢
⎢
CH3─CH─CH─CH3
Name the longest continuous chain.
methyl groups
CH3
CH3 CH3
⎢
⎢
CH3─CH─CH─CH3
CH3
CH3 CH CH2 CH CH3
2,4-dimethylpentane
butane
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36
Naming Alkanes
Give the name of
Learning Check
CH3 CH3
⎢
⎢
CH3─CH─CH─CH3
Write the name of
Cl CH3
⎢
⎢
CH3─CH2─CH─CH─CH3
Number chain.
CH3 CH3
⎢
⎢
CH3─CH─CH─CH3
1
2
3 4
STEP 3: Locate substituents and name.
2,3-dimethylbutane
STEP 2:
37
Solution
38
Learning Check
STEP 1:
Longest chain is pentane.
Give the IUPAC name for each of the following:
STEP 2:
Number chain from end nearest substituent.
Cl CH3
⎢
⎢
CH3─CH2─CH─CH─CH3
5
4
3
2
1
A.
CH3
CH3
|
|
CH3─CH─CH2 ─CH─CH3
B.
Cl
CH3
|
|
CH3─CH2─CH─CH2─C─CH2─CH3
|
Cl
STEP 3: Locate substituents and name alphabetically.
3-chloro-2-methylpentane
39
Guide to Drawing Alkane
Formulas
Solution
A.
CH3
CH3
|
|
CH3─CH─CH2 ─CH─CH3
1
B.
2
40
3
4
2,4-dimethylpentane
5
Cl
CH3 more substituents on C3
|
|
CH3─CH2─CH─CH2─C─CH2─CH3
|
Cl
7
6
5
4
3
2
1
3,5-dichloro-3-methylheptane
41
42
Learning Check
Solution
3-bromo-1-chlorobutane
STEP 1: Longest chain has 4 carbon atoms.
C─C─C─C
STEP 2: Number chain and add substituents.
Br
⎢
C ─ C ─ C ─ C ─ Cl
4 3 2
1
STEP 3: Add hydrogen to complete 4 bonds to each C.
Br
⎢
CH3─CH─CH2─CH2─Cl
Draw the condensed structural formula for
3-bromo-1-chlorobutane.
43
Naming Cycloalkanes with
Substituents
44
Learning Check
Name each of the following.
The name of a substituent is placed in front of the
cycloalkane name.
1.
2.
chlorocyclopentane
CH3
CH3
methylcyclobutane
CH2─CH3
Cl
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46
Chapter 10 Introduction to Organic
Chemistry: Alkanes
Solution
Name each of the following.
10.4
Properties of Alkanes
1. methylcyclopropane
2. ethylcyclohexane
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48
Some Properties of Alkanes
Some Properties of Alkanes
Alkanes are
• nonpolar.
• insoluble in water.
• less dense than water.
• flammable in air.
Alkanes with 1-4 carbon
atoms are
• methane, ethane,
propane, and butane.
• gases at room
temperature.
• used as heating fuels.
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Some Properties of Alkanes
50
Some Properties of Alkanes
Alkanes with 18 or more carbon atoms
• have high molar masses.
• are waxy solids at room temperature.
• used in waxy coatings of fruits and
vegetables.
Alkanes with 5-8 carbon atoms are
• liquids at room temperature.
• pentane, hexane, heptane, and octane.
• very volatile.
• used to make gasoline.
Alkanes with 9-17 carbon atoms
• are liquids at room temperature
• have higher boiling points.
• are found in kerosene, diesel, and jet fuels.
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51
Combustion
52
Learning Check
Write a balanced equation for the
complete combustion of propane.
In combustion reactions,
• alkanes react with oxygen.
• CO2, H2O, and energy are produced.
• Alkane + O2
CO2 + H2O + heat
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54
Chapter 10 Introduction to Organic
Chemistry: Alkanes
Solution
10.5
Functional Groups
Unbalanced equation
C3 H8 + O 2
CO2 + H2O
Balance C
C3 H8 + O 2
3CO2 + H2O
Balance H
C3 H8 + O 2
3CO2 + 4H2O
Balance O
C3H8 + 5O2
3CO2 + 4H2O (Balanced)
55
Elements in Organic Compounds
56
Functional Groups
In organic molecules, carbon atoms bond
• with four bonds.
• mostly with H and other C atoms.
• sometimes to O, N, S.
• sometimes to halogens F, Cl, and Br.
Functional groups are
• a characteristic feature of organic molecules that
behave in a predictable way.
• composed of an atom or group of atoms.
• groups that replace a hydrogen atom in the
corresponding alkane.
• a way to classify families of organic compounds.
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58
Comparing Alkenes, Alkynes,
and Aromatic Compounds
Alkenes, Alkynes, and Aromatic
Compounds
Alkenes contain a double bond between adjacent
carbon atoms.
Alkynes contain a triple bond.
Aromatic compounds contain a ring of six carbon
atoms called benzene.
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60
Alcohols and Ethers
Aldehydes and Ketones
A thiol contains the thiol
(-SH) functional group.
An aldehyde contains a
carbonyl group (C=O), which
is a carbon atom with a double
bond to an oxygen atom. The
carbonyl is attached to a
hydrogen.
An ether contains an
oxygen atom bonded to
two carbon atoms.
In a ketone, the carbon of the
carbonyl group (C=O) is
attached to two carbon atoms.
An alcohol contains the
hydroxyl (-OH) functional
group.
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61
Carboxylic Acids and Esters
62
Amines and Amides
Carboxylic acids contain the
carboxyl group, which is a
carbonyl group attached to a
hydroxyl group.
O
║
— C—OH
An ester contains the
carboxyl group between
carbon atoms.
In amines, the functional
group is a nitrogen atom.
|
—N —
Amines
In amides, the hydroxyl
group of a carboxylic acid
is replaced by a nitrogen
group.
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An amide
63
Summary of Functional Groups
64
Learning Check
Classify each of the following as: alcohol, ether,
aldehyde, ketone, carboxylic acid, ester, amine, or
amide.
1) CH3─CH2─CH2─OH
2) CH3─O─CH2─CH3
3) CH3─CH2─NH2
O
║
4) CH3─C─OH
O
║
5) CH3─C─O─CH3
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66
Solution
1) CH3─CH2─CH2─OH
2) CH3─O─CH2─CH3
3) CH3─CH2─NH2
alcohol
ether
amine
O
║
4) CH3─C─OH
carboxylic acid
O
║
5) CH3─C─O─CH3
ester
67