1 Chapter 11 Introduction to Organic Chemistry: Alkanes 11.1 Organic Compounds Copyright © 2007 by...

1

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.

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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)Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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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?


5

Comparing Organic and Inorganic Compounds

TABLE 11.1

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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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

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

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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

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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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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


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 StructuresTABLE 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.

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cumming

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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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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.


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.

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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

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Naming SubstituentsIUPAC

Fluoro

Chloro

Bromo

Iodo

Hydroxy

F

Cl

Br

I

OH

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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

|

Cl 7 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 hexaneLocation 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 4STEP 3 Add hydrogen to complete 4 bonds to each C.

Br CH3─CH─CH2─CH2─Cl

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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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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 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

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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

BPs of alkanes Are lowest of

organic compounds. Increase with larger

molecules due to increased dispersion forces.

Decrease for branched alkanes.

Increase for cycloalkanes.

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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 incrude 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 Organic Chemistry

11.5

Functional Groups


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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.

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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 H in the corresponding

alkane. A way to classify families of organic compounds.

Functional Groups

80

Some Functional Groups

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Alkenes and Alkynes

Alkenes contain a double bond between adjacent carbon atoms.

Alkynes contain a triple bond.


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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More Functional Groups

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.


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.


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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Summary of Functional Groups

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Functional Groups in Everyday Items

Methyl amine (fish)


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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

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Solution

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

alcohol ether

3) CH3─CH2─NH2 amine O O || ||

4) CH3─C─OH 5) CH3─C─O─CH3

carboxylic acid ester

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