chapter 11 introduction to organic chemistry:...

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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

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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?



5

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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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

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.

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

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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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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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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.

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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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

chapter 11 introduction to organic chemistry:...

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