Alkanes

Organic Chemistry

Timberlake LecturePLUS 2

Alkanes

Contain C and H only

Contain single bonds C-C

Have 4 bonds to every carbon (C) atom

Are nonpolar

Timberlake LecturePLUS 3

Complete Structural Formulas

Show the bonds between each of the atoms

H H

H C H H C H H H

CH4 , methane

Timberlake LecturePLUS 4

More Alkanes

H H Condensed Structural Formulas

H C C H CH3 CH3

H H Ethane

H H H

H C C C H CH3 CH2 CH3

H H H Propane

Timberlake LecturePLUS 5

IUPAC Names

Name # carbons Structural Formula

Methane 1 CH4

Ethane 2 CH3CH3

Propane 3 CH3CH2CH3

Butane 4 CH3CH2CH2CH3

Pentane 5 CH3CH2CH2CH2CH3

Timberlake LecturePLUS 6

IUPAC NAMES

Name # carbons Structural Formula

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

AlkanesAlkanes are a family of hydrocarbons containing only single bonds between

the carbon atoms

Methane

Tetrahedral

Expanded structural formula: showing each bond line.

CH4Molecular formula

Ethane

C2H6 Molecular formula

Expanded structural formula

CH3 – CH3

Condensed structural formula: with each carbon atom and

its attached hydrogen atoms.

Alkanes

Homologous Series general formulaCnH2n+2

n: number of carbon atoms

Naming of Alkanes

CnH2n+2Prefix + ane

No of C atoms Prefix1 meth-2 eth-3 prop-4 but-5 pent-6 hex-7 hept-8 oct-9 non-

10 dec-

• Carbon-to-carbon chains can be (A) straight, (B) branched, or (C) in a closed ring.

• (Some carbon bonds are drawn longer, but are actually the same length.)

Review

• Work through the Sample Problem page 175

• Complete the revision questions page 175 (1 – 3)

Timberlake LecturePLUS 15

Learning Check Alk1

A. What is the condensed formula for H H H H

H C C C C H

H H H H

B. What is its molecular formula?C. What is its name?

Timberlake LecturePLUS 16

Solution Alk1

A. CH3CH2CH2CH3

B. C4H10

C. butane

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Reactions of Alkanes

• Alkanes burn in oxygen to form carbon dioxide and water - oxidation or combustion reaction

• CH4(g) + O2(g) CO2(g) + 2H2O(g)

• Alkanes react with chlorine or fluorine in a reaction called a substitution reaction (one of the chlorine or fluorine atoms takes the place of one or more of the hydrogen atoms

Timberlake LecturePLUS 18

Reactions of Alkanes

Combustion

alkane + O2 CO2 + H2O + heat

Timberlake LecturePLUS 19

Combustion In the Cell

Metabolic oxidation is combustion

C6H12 O6 + 6O2 6CO2 + 6H2O + heat

glucose

Timberlake LecturePLUS 20

Learning Check Alk2

Complete the combustion reaction for

C3H8 + O2 +

Balance your equation

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Solution Alk2

Step 1

C3H8 + O2 CO2 + H2O

Step 2

C3H8 + O2 3 CO2 + 4 H2O

Step 3

C3H8 + 5 O2 3 CO2 + 4 H2O

Timberlake LecturePLUS 22

Learning Check Alk3

Complete and balance the reaction for the complete combustion of C7H16

Timberlake LecturePLUS 23

Solution Alk3

Step 1

C7H16 + O2 CO2 + H2O

Step 2

C7H16 + O2 7 CO2 + 8 H2O

Step 3

C7H16 + 11 O2 7 CO2 + 8 H2O

Review

• Complete the revision questions page 175 (4 - 6)

Isomers• Straight chain alkanes: An alkane that has all its carbons connected in a row.• Branched chain alkanes: An alkane that has a branching connection of carbons.• Isomers: Compounds with same molecular formula but different structures.

• There is only one possible way that the carbons in methane (CH4), ethane (C2H6), and propane (C3H8) can be arranged.

• However, carbons in butane (C4H10) can be arranged in two ways; four carbons in a row (linear alkane) or a branching (branched alkane). These two structures are two isomers for butane.

29

Butane

Different isomers are completely different compounds. They have different structures, different physical properties such as melting point and boiling point, and may have different physiological properties.

Timberlake LecturePLUS 31

Review

• Complete revision questions page 176 (7 – 9)