1 chapter 10 introduction to organic chemistry: alkanes 10.1 organic compounds
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Chapter 10 Introduction to Organic Chemistry: Alkanes
10.1 Organic Compounds
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Organic Chemistry
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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Organic Compounds
Typical organic compounds
• 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 organic,but NaCl is not?
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Comparing Organic and Inorganic Compounds
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Writing Formulas for Alkanes
In organic compounds, • carbon has 4 valence electrons and hydrogen has 1.
• • C • H • •
• carbon achieves an octet by forming four bonds. H H
H C H H C H
H H CH4, methane
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Organic Chemistry’s Golden Rule:
Carbon always forms 4 bonds.
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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 Molecules
In organic molecules, • valence electrons are shared.• covalent bonds form between carbon 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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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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Expanded and Condensed Structures
Copyright © 2009 by Pearson Education, Inc.
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Structural Formulas
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 CH3─CH2─CH2─CH3
│ │ │ │ H H H H
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Lewis structure Structural formula Condensed structural formula
Line structure Ball-and-stick model Space-f illng model
Types of formulas and models used to represent organic molecules. Each diagram is a representation of a propane
molecule.
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C C C C C CC C CH H
H
H H
H
H
H
Structural formula Skeleton formula Modified Skeleton formula
Remove H’s Remove H bonds
Line structure
Remove C’s
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( condensed structural f ormula)
( line structure)
This is an example of how to change a condensed formulainto a line structure.
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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:
Name # Carbons Condensed Structural ______Formula_______
Methane1 CH4
Ethane 2 CH3―CH3
Propane 3 CH3―CH2―CH3
Butane 4 CH3―CH2―CH2―CH3
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Names of Alkanes
Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.Name # Carbons Structural Formula
Pentane 5 CH3CH2CH2CH2CH3
Hexane 6 CH3CH2CH2CH2CH2CH3
Heptane 7 CH3CH2CH2CH2CH2CH2CH3
Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3
Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
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Writing Structural Formulas
Carbon atoms in a chain
• maintain tetrahedral shape.• are connected in a zigzag pattern.• are drawn as 2-dimensional. • can be written in several conformations.
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Some Structures for Butane
Copyright © 2009 by Pearson Education, Inc.
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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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Cycloalkanes
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.
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Cycloalkanes
The structural formulas of cycloalkanes are usually represented by geometric figures.
More Cycloalkanes
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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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Chapter 10 Introduction to Organic Chemistry: Alkanes
10.3 Alkanes with Substituents
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Isomers of Butane
Isomers• have the same
molecular formula.• have different atom
arrangements.
• of butane (C4H10) are a straight chain and a branched chain.
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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.
CH3 methyl
CH3 CH2 ethyl
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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.
Guide to Naming Alkanes
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Alkanes with Substituents
CH3
CH3 CH CH3 methylpropane
methyl groups
CH3 CH3
CH3 CH CH2 CH CH3 2,4-dimethylpentane
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Naming Alkanes
Give the name of CH3 CH3
CH3─CH─CH─CH3
STEP 1: Name the longest continuous chain. CH3 CH3
CH3─CH─CH─CH3
butane
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Naming Alkanes
Give the name of CH3 CH3
CH3─CH─CH─CH3
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
Give the IUPAC name for each of the following:
A. CH3 CH3
| |
CH3─CH─CH2 ─CH─CH3
B. Cl CH3 | |
CH3─CH2─CH─CH2─C─CH2─CH3
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Cl
Guide to Drawing Alkane Formulas
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Learning Check
Draw the condensed structural formula for 3-bromo-1-chlorobutane.
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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 1STEP 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 thecycloalkane name.
methylcyclobutane CH3
chlorocyclopentane Cl
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Learning Check
Name each of the following.
1. CH3
CH2─CH3
2.
Alkyl Halides
Alkyl halides are organohalogens that have the halogen atom attached to an alkyl group.
They are represented by R–X
Naming Alkyl Halides
CH3CHBrCH2Br
1,2-dibromopropane
CH2Cl2
dichloromethane(methylene chloride)
CHCl3trichloromethane(chloroform)
CH3Br
bromomethane(methyl bromide)
CCl4tetrachloromethane(carbon tetrachloride)
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Chapter 10 Introduction to Organic Chemistry: Alkanes
10.4 Properties of Alkanes
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Some Properties of Alkanes
Alkanes are• nonpolar.• insoluble in water.• less dense than water.• flammable in air.
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Some Properties of Alkanes
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
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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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.
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Combustion
In combustion reactions,• alkanes react with oxygen.
• CO2, H2O, and energy are produced.
• Alkane + O2 CO2 + H2O + heat
Copyright © 2009 by Pearson Education, Inc.
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Chapter 10 Introduction to Organic Chemistry: Alkanes
10.5 Functional Groups
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Elements in Organic Compounds
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.
Copyright © 2009 by Pearson Education, Inc.
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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.
Functional Groups
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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.
An alkene(olefins)
An alkyne(acetylenes)
An aromatic(benzenes)
Comparing Alkenes, Alkynes, and Aromatic Compounds
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Alcohols and Ethers
An alcohol contains the hydroxyl (-OH) functional group.
A thiol contains the thiol (-SH) functional group.
An ether contains an oxygen atom bonded to two carbon atoms.
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Aldehydes and Ketones
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.
In a ketone, the carbon of the carbonyl group (C=O) is attached to two carbon atoms.
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Carboxylic Acids and Esters
Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.
O ║
— C—OHAn ester contains the carboxyl group between carbon atoms.
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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.
Amines
An amide
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Summary of Functional Groups