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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

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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

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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

|

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

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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

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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.

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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