Chapter 11 Introduction to Organic Chemistry:...
Transcript of Chapter 11 Introduction to Organic Chemistry:...
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Chapter 11 Introduction to
Organic Chemistry: Alkanes
11.1
Organic Compounds
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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.
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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)
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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?
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Comparing Organic and Inorganic
Compounds
TABLE 11.1
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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
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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
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Writing Formulas for Carbon
Compounds
In 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
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Tetrahedral Structure of Carbon
� VSEPR theory predicts that a
carbon atom
with four single, covalent bonds
has a tetrahedral
shape.
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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
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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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Chapter 11 Introduction to
Organic Chemistry: Alkanes
11.2
Alkanes
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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.
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IUPAC Names for Alkanes
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TABLE 11.2
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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.
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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
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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
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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.
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Expanded and Condensed
Structures
TABLE 11.3
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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.
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Conformations
The groups attached to a C-C single bond
� Rotate around the bond,
� Give different relative arrangements called conformations.
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Conformations of Butane
� Rotation of the end CH3- provides different conformations for butane.
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Some Structures for Butane
TABLE 11.3
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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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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?
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Solution
A. CH3CH2CH2CH2CH3
B. C5H12
C. pentane
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Learning Check
Write the condensed structural formula for
A. ethane
B. heptane
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Solution
Write the condensed structural formula for
A. ethane CH3─CH3
B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3
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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.
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Cycloalkanes
The structural formulas of cycloalkanes are usually
represented by geometric figures,
Cyclopropane CH2
CH2 CH2
CyclobutaneCH2 CH2
CH2 CH2
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More Cycloalkanes
Cyclopentane CH2
CH2 CH2
CH2 CH2
Cyclohexane
CH2
CH2 CH2
CH2 CH2
CH2
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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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Solution
Name the following:
A. CH3─CH2─CH2─CH3 butane
B. cyclopropane
C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 octane
D.
cyclohexane
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Chapter 11 Introduction to Organic
Chemistry: Alkanes
11.4
Properties of Alkanes
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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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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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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.
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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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Boiling Points of Pentanes
Boiling points of alkanes
� Are lowest of organic compounds.
� Increase with larger molecules due to increased dispersion forces.
� Decrease for branched alkanes.
� Increase for cycloalkanes.
TABLE 11.6
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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
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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
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Crude Oil
The hydrocarbons in crude oil are
� Separated by boiling points.
� Heated to higher temperatures to produce gases that can be removed and cooled.
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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
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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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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
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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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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)
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Write a balanced equation for the reaction for the complete combustion of heptane C7H16.
Learning Check
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C7H16 + O2 CO2 + H2O
C7H16 + O2 7CO2 + 8H2O
C7H16 + O2 7CO2 + 8H2O
C7H16 +11O2 7CO2 + 8H2O
Balanced equation:
C7H16 + 11O2 7CO2 + 8H2O
Solution
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Write the combustion reaction for ethane and balance.
Learning Check
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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
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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
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Learning Check
Give the structures and names of the possible monosubstituted products for the reaction of
propane with bromine in the presence of light.
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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
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Chapter 11 Introduction to
Organic Chemistry: Alkanes
11.3
Alkanes with Substituents
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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.
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branch
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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
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Naming Substituents
In the IUPAC system,
� A carbon branch is
named as an alkyl group.
� Halogen atoms are
named as halo.
TABLE 11.5
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Alkanes with Alkyl Groups
CH3
CH3 CH CH3 methylpropane
methyl groups
CH3 CH3
CH3 CH CH2 CH CH3 2,4-dimethylpentane
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Naming Alkanes with Substituents
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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
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Learning Check
Write the IUPAC name for
Cl CH3
CH3─CH2─CH─CH─CH3
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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
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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
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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
|
Cl7 6 5 4 3 2 1
3,5-dichloro-3-methylheptane
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Drawing Alkane Structures
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What is In A Name?
The structural formula is drawn from the IUPAC name.
2, 4-dimethylhexane
2, 4 dimethyl hexane
Location of Two CH3- groups 6 carbon main chain
branches on attached with single C-C bonds
main chain
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Learning Check
Draw the condensed structural formula for
2-bromo-4-chlorobutane.
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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 4
STEP 3 Add hydrogen to complete 4 bonds to each C.
Br
CH3─CH─CH2─CH2─Cl
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Naming Cycloalkanes with
Substituents
The 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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Learning Check
Name each of the following:
1. CH3
CH2─CH3
2.
Cl
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Solution
Name each of the following:
1. methylcyclopropane
2. 3-chloro-1-ethylcyclohexane
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Write three isomers of C5H12 and name each.
Learning Check
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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 branchCH3
│CH3─CH─CH2─CH3 2-methylbutane
A chain of 3 carbon atoms and 2 carbon branchesCH3
│CH3─CH─CH3 2,2-dimethylpropane
│CH3
Solution