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Chapter 11 Introduction to Organic Chemistry: Alkanes
11.1
Organic Compounds
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
2
Organic Compounds
An organic compound 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.
3
Properties of Organic Compounds
Typical organic compounds
Contain carbon.
Have covalent bonds.
Have low melting points.
Have low boiling points.
Are flammable.
Are soluble in nonpolar solvents.
Are not soluble in water.
Oil (organic) and
water (inorganic)Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
4
Organic vs. Inorganic
Propane, C3H8, is an organic compound used as a fuel.
NaCl, salt, is an inorganic compound composed of Na+ and Cl− ions.
Why is propane an
organic compound, but
NaCl is not?
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
5
Comparing Organic and Inorganic Compounds
TABLE 11.1
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6
Learning Check
Identify each characteristic as most typical of
compounds that are (I) inorganic or (O) organic.
1. Has a high melting point
2. Is not soluble in water
3. Has a formula CH3─CH2─CH3
4. Has a formula MgCl2
5. Burns easily in air
6. Has covalent bonds
7
Solution
Identify each characteristic as most typical of
compounds that are (I) inorganic or (O) organic.
I 1. Has a high melting point
O 2. Is not soluble in water
O 3. Has a formula CH3─CH2─CH3
I 4. Has a formula MgCl2
O 5. Burns easily in air
O 6. Has covalent bonds
8
Writing Formulas for Carbon CompoundsIn carbon compounds Carbon has 4 valence electrons and hydrogen has 1.
•
• C • H •
•
To achieve an octet, C forms four bonds. H H
H C H H C H
H H CH4 , methane
9
Tetrahedral Structure of Carbon
VSEPR theory predicts that a carbon atom with four single, covalent bonds has a tetrahedral shape.
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10
Organic Compounds with More Carbon Atoms In organic molecules with more carbon atoms, Valence electrons are shared. Covalent bonds form between carbon and carbon atoms. Covalent bonds form between carbon and hydrogen
atoms. H H H H • • • •
H C C H H C C H
• • • • H H H H
ethane, CH3─CH3
11
Tetrahedral Structure of Carbon
In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.
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12
Chapter 11 Introduction to Organic Chemistry: Alkanes
11.2
Alkanes
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
13
Names of Alkanes
The names of alkanes Are determined by the IUPAC (International Union of
Pure and Applied Chemistry) system. Use a prefix to indicate the number of carbons in a
chain. End in –ane.
14
IUPAC Names for Alkanes
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TABLE 11.2
15
Learning Check
A. Give the name of each compound:
1) CH3—CH3
2) CH3—CH2—CH3
3) CH3—CH2—CH2—CH2—CH2—CH3
B. Write the condensed structural formula of
pentane.
16
Solution
A. Give the name of each compound:
1) CH3—CH3 ethane
2) CH3—CH2—CH3 propane
3) CH3—CH2—CH2—CH2—CH2—CH3
hexane
B. Write the condensed structural formula of pentane.
CH3—CH2—CH2—CH2—CH3
17
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 Condensed
H
H C H CH4 , methane
H
18
Writing Structural Formulas
Carbon atoms in a chain Maintain tetrahedral shape. Are connected in a zig-zag pattern. Are drawn as 2-dimensional. Can be written in several conformations.
19
Expanded and Condensed StructuresTABLE 11.3
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20
Line-Bond Formulas
Because each C atom has a tetrahedral arrangement, the order of atoms is not a straight line, but a zigzag pattern.
A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds from carbon atom to carbon atom.
21
Conformations
The groups attached to a C-C single bond
Rotate around the bond,
Give different relative arrangements called conformations.
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22
Conformations of Butane
Rotation of the end CH3- provides different conformations for butane.
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23
Some Structures for Butane
TABLE 11.3
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24
Hexane has Six Carbon Atoms
Hexane Is an alkane with 6 carbon atoms in a continuous
chain. Has a “zig-zag” look because each carbon atom is
at the center of a tetrahedron. Is represented by a ball-and-stick model as
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25
Learning Check
A. Write the condensed formula for:
H H H H H
H C C C C C H
H H H H H
B. What is its molecular formula?
C. What is its name?
28
Solution
Write the condensed structural formula for
A. ethane CH3─CH3
B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3
29
Cycloalkanes
Cycloalkanes Are cyclic alkanes. Have 2H 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.
30
Cycloalkanes
The structural formulas of cycloalkanes are usually
represented by geometric figures,
Cyclopropane CH2
CH2 CH2
CyclobutaneCH2
CH2
CH2 CH2
33
Solution
Name the following:
A. CH3─CH2─CH2─CH3 butane
B. cyclopropane
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 octane
D. cyclohexane
34
Chapter 11 Introduction to Organic Chemistry: Alkanes
11.3
Alkanes with Substituents
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35
Isomers of Butane
Isomers Have the same
molecular formula.
Have different atom arrangements.
Of butane (C4H10) consist of a straight chain and a branched chain each with 4 carbon atoms.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
branch
36
Alkyl groups
Alkyl groups are Alkanes that are missing one H. Substituents attached to carbon chains. Named with a –yl ending. H
H C CH3 methyl H H H H C C CH3 CH2 ethyl H H
37
Naming Substituents
In the IUPAC system, A carbon branch is
named as an alkyl group.
Halogen atoms are named as halo.
38
Naming SubstituentsCH3
CH2 CH3
CH2 CH2 CH3
CHCH3
CH3
CH2 CH
CH3
CH3
CH2 CH2 CH2 CH3
CH
CH3
CH2 CH3
C
CH3
CH3
CH3
IUPAC Common
methyl methyl
ethyl ethyl
propyl n-propyl
1-methylethyl Isopropyl
butyl n-butyl
1-methylpropyl sec-butyl
2-methylpropyl Isobutyl
1,1-dimethylethyl tert-butyl ort-butyl
40
Alkanes with Alkyl Groups
CH3
CH3 CH CH3 methylpropane
methyl groups
CH3 CH3
CH3 CH CH2 CH CH3 2,4-dimethylpentane
41
Naming Alkanes with Substituents
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42
Guide to Naming Alkanes
Give the name of CH3 CH3
CH3─CH─CH─CH3
STEP 1 Longest chain is butane.
STEP 2 Number chain. CH3 CH3
CH3─CH─CH─CH3
1 2 3 4
STEP 3 Locate substituents and name.
2,3-dimethylbutane
44
Solution
STEP 1 Longest chain is pentane.
STEP 2 Number chain from end nearest substituent. Cl CH3 (nearest end)
CH3─CH2─CH─CH─CH3
5 4 3 2 1
STEP 3 Locate substituents and name alphabetically.
3-chloro-2-methylpentane
45
Learning Check
Give the IUPAC name for each of the following:
A. CH3 CH3
| |
CH3─CH─CH2 ─CH─CH2─CH3
B. Cl CH3
| |
CH3─CH2─CH─CH2─C─CH2─CH3
|
Cl
46
Solution
A. CH3 CH3
| | CH3─CH─CH2 ─CH─CH2─CH3 2,4-dimethylhexane 1 2 3 4 5 6
B. 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
47
Drawing Alkane Structures
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48
What is In A Name?
The structural formula is drawn from the IUPAC name.
2, 4-dimethylhexane
2, 4 dimethyl hexaneLocation of Two CH3- groups 6 carbon main chain
branches on attached with single C-C bonds
main chain
50
Solution
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
1 2 3 4STEP 3 Add hydrogen to complete 4 bonds to each C.
Br CH3─CH─CH2─CH2─Cl
51
Naming Cycloalkanes with SubstituentsThe name of a substituent is placed in front of the
cycloalkane name.
CH3
methylcyclobutane
Number ring with two substituents
1-bromo-2-chlorocyclopentane
Br
Cl
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A chain of 5 carbon atoms CH3─CH2─CH2─CH2─CH3
pentane
A chain of 4 carbon atoms and 1 carbon branch CH3
│CH3─CH─CH2─CH3 2-methylbutane
A chain of 3 carbon atoms and 2 carbon branches CH3
│CH3─CH─CH3 2,2-dimethylpropane
│ CH3
Solution
56
Chapter 11 Introduction to Organic Chemistry: Alkanes
11.4
Properties of Alkanes
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
57
Some Properties of Alkanes
The properties of alkanes include
being Nonpolar. Insoluble in water. Less dense than water Flammable in air.
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58
Alkanes with 1-4 Carbon Atoms
Alkanes with 1-4 carbon atoms are Methane, ethane, propane, and
butane. Gases at room temperature. Used as heating fuels.
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59
Alkanes with 5-17 Carbon Atoms
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.
60
Alkanes with 18 or more Carbon Atoms
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.
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61
Boiling Points of Pentanes
BPs of alkanes Are lowest of
organic compounds. Increase with larger
molecules due to increased dispersion forces.
Decrease for branched alkanes.
Increase for cycloalkanes.
62
Learning Check
For the following pairs of hydrocarbon, which one has
the higher boiling point? Why?
1. butane or octane
2. hexane or 2,3-dimethylbutane
63
Solution
For the following pairs of hydrocarbon, which one has
the higher boiling point? Why?
1. butane or octane octane has more carbon atoms
2. hexane or 2,3-dimethylbutane
hexane is not branched
64
Crude Oil
The hydrocarbons incrude oil are Separated by
boiling points. Heated to higher
temperatures to produce gases that can be removed and cooled.
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65
Classification of Carbon Atoms
The classification of carbon atoms indicates the
number of carbon atoms attached. A primary carbon (1°) bonds to one carbon atom. A secondary carbon (2°) bonds to two carbon atoms. A tertiary carbon (3°) bonds to three carbon atoms.
CH3
|
CH3 —CH2—CH2—CH3 CH3—CH—CH3
primary secondary tertiary
66
Combustion of Alkanes
Alkanes
Undergo combustion by reacting with oxygen to produce carbon dioxide, water, and energy.
Are typically not very reactive due to strong C-C single bonds.
alkane + O2 CO2 + H2O + energy
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67
Write the equation
C5H12 + O2 CO2 + H2O
Balance C
C5H12 + O2 5CO2 + H2O
Balance H
C5H12 + O2 5CO2 + 6H2O
Balance O with O2
C5H12 + 8O2 5CO2 + 6H2O balanced
Balancing A Combustion Equation
68
Learning Check
Propane is used to provide heat for
cooking or warming a room. Write a
balanced equation for the complete
combustion of propane.
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69
Solution
Unbalanced equation
C3H8 + O2 CO2 + H2O
Balance C
C3H8 + O2 3CO2 + H2O
Balance H
C3H8 + O2 3CO2 + 4H2O
Balance O
C3H8 + 5O2 3CO2 + 4H2O (Balanced)
70
Write a balanced equation for the reaction for the complete combustion of heptane C7H16.
Learning Check
71
C7H16 + O2 CO2 + H2O
C7H16 + O2 7CO2 + 8H2O
C7H16 + O2 7CO2 + 8H2O
C7H16 +11O2 7CO2 + 8H2O
Balanced equation:
C7H16 + 11O2 7CO2 + 8H2O
Solution
73
Write the combustion reaction for ethane and balance.ethane CH3CH3 = C2H6
C2H6 + O2 2CO2 + 3H2O
C2H6 + 7 O2 2CO2 + 3H2O
C2H6 + 7/2 O2 2CO2 + 3H2O Multiply through by 2 to clear
2C2H6 + 7O2 4CO2 + 6H2O balanced
Solution
74
Halogenation of Alkanes (Substitution)
When alkanes react with halogens,
The reaction is called substitution, one or more H atoms are replaced with a halogen usually Cl or Br.
Light or heat is required.
A mixture of halogenated products result, but we write the
equation with the monosubstituted product.
Example: ethane and chloride
light
CH3—CH3 + Cl2 CH3—CH2 —Cl
75
Learning Check
Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.
76
Solution
Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.
CH3—CH2—CH2— Br
1-bromopropane; propyl bromide
Br
|
CH3—CH—CH3
2-bromopropane; isopropyl bromide
77
Chapter 11 Organic Chemistry
11.5
Functional Groups
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78
Elements in Organic Compounds
In organic molecules,
C atoms form bonds Mostly with H and
other C atoms. Sometimes atoms
of O, N, S, and halogens F, Cl, and Br.
79
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 H in the corresponding
alkane. A way to classify families of organic compounds.
Functional Groups
81
Alkenes and Alkynes
Alkenes contain a double bond between adjacent carbon atoms.
Alkynes contain a triple bond.
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82
Alcohols and Ethers
An alcohol contains the hydroxyl (-OH) functional group.
In an ether, an oxygen atom is bonded to two carbon atoms
–C–O–C– .
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84
Aldehydes and Ketones
An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen.
In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms.
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85
Carboxylic Acids and Esters
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.
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86
Amines and Amides
In amines, the functional group is a nitrogen atom.
|
—N —
In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group.
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88
Functional Groups in Everyday Items
Methyl amine (fish)
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89
Learning Check
Classify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine.
1) CH3–CH2–CH2–OH
2) CH3–O–CH2–CH3
3) CH3–CH2–NH2
O O || ||
4) CH3–C–OH 5) CH3–C–O–CH3