Chapter 10 Introduction to

Organic Chemistry: Alkanes

1

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

• usually has carbon written first

2

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

Vegetable oil is an organic compound

and not soluble in water.

3

Comparing Organic and

Inorganic Compounds

4

Bonding in Organic Compounds

In organic compounds,

• carbon has 4 valence electrons and hydrogen has 1

• carbon achieves an octet by forming four bonds, with each

line representing 2 electrons

CH4, methane

5

C + 4 H C HH

H

H

C HH

H

H

C

H

H

H H

Tetrahedral Structure of Carbon CH4

VSEPR theory predicts that

a carbon atom with four

single, covalent bonds has a

tetrahedral shape.

Methane is represented

using different models:

(a) tetrahedron, (b) ball-and-

stick model, (c) space-filling

model, (d) expanded

structural formula.

6

Tetrahedral Structure of Carbon C2H6

In ethane,

• each carbon forms covalent bonds to another carbon and three hydrogen atoms

• each carbon atom retains its tetrahedral shape

Ethane, CH3─CH3

7

CH

H

HC

H

H

H CC H

H

H

H

H

H

In molecules with two or more

carbon atoms, each carbon atom

with four single bonds has a

tetrahedral shape.

Representations of ethane:

(a) tetrahedral shape of each

carbon, (b) ball-and-stick

model, (c) space-filling model,

(d) expanded structural formula.

8

Tetrahedral Structure of Carbon C2H6

Learning Check

In the butane molecule, C4H10, predict the shape around each

carbon atom.

9

C

H

H

H C

H

H

C

H

H

C

H

H

H

Solution

In the butane molecule, C4H10, predict the shape around each carbon atom.

Each carbon atom has four single covalent bonds and therefore a tetrahedral shape.

10

C

H

H

H C

H

H

C

H

H

C

H

H

H

Alkanes

Alkanes are organic molecules

• containing primarily C–C single bonds

• commonly used as fuels for heaters and cooktops

• whose names end in ane

• named by using the number of carbon atoms connected in a continuous chain

11

IUPAC Naming of the First Ten Alkanes

12

Condensed Structural Formulas

In a condensed structural formula,

• each carbon atom and its attached hydrogen atoms are

written as a group

• a subscript indicates the number of hydrogen atoms bonded

to each carbon atom

• of butane, four carbon atoms are attached in a straight line

CH3CH2CH2CH3 butane

13

Condensed 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 Expanded

Condensed

14

C

H

H

H CH3= C

H

H

CH2=

Writing Structural Formulas

Carbon atoms in a chain

• maintain tetrahedral shape

• are connected in a zigzag pattern

• are drawn as two-dimensional

• can be written in several conformations

15

Expanded, Condensed,

and Skeletal Structures

16

A hexane molecule can

be represented in several ways:

• a molecular formula

• a ball-and-stick model

• an expanded structural formula

• a condensed structural formula

• a skeletal formula

Learning Check

Write the condensed structural formula for

A. ethane

B. heptane

17

Solution

Write the condensed structural formula for

A. ethane CH3CH3

B. heptane CH3CH2CH2CH2CH2CH2CH3

18

Cycloalkanes

Cycloalkanes

• are cyclic alkanes

• have two less hydrogen atoms 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

propane, C3H8 cyclopropane, C3H6

19

H2C

H2C

CH2H3C

H2C

CH3

CnH(2n+2) CnH2n

Formulas of Cycloalkanes

20

Learning Check

Name the following alkanes:

A. CH3CH2CH2CH3

B.

C. CH3CH2CH2CH2CH2CH2CH2CH3

D.

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Solution

Name the following alkanes:

A. CH3CH2CH2CH3 butane

B. cyclopropane

C. CH3CH2CH2CH2CH2CH2CH2CH3 octane

D. cyclohexane

22

Substitutions - Isomers

Isomers

• have the same molecular

formula with different atom

arrangements

• of butane (C4H10) are a straight

chain and a branched chain

The isomers of butane have the

same number and type of atoms,

but the atoms are bonded in a

different order.

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Substituents and Alkyl Groups

Substituents are atoms or groups of atoms attached to the

carbon chain and include alkyl and halo groups.

Alkyl groups are

• carbon branches attached to carbon chains

• named with a yl ending

Halo substituents are

• halogens attached to the carbon chain

• named as fluoro, chloro, bromo, or iodo

24

Substituents and Alkyl Groups

25

Guide to Naming Alkanes

with Substituents

26

Write IUPAC Names for Alkanes

with Substituents

Give the IUPAC name for the following compound:

Step 1 Write the alkane name of the longest chain of

carbon atoms.

The longest chain has

five carbons, pentane.

27

C

H

H

C

Cl

H

C

H

CH3

CH C

H

H

H

H

H

C

H

H

C

Cl

H

C

H

CH3

CH C

H

H

H

H

H

Write IUPAC Names for Alkanes with

Substituents

Step 2 Number the carbon atoms starting from the end

nearer a substituent.

Step 3 Give the location and name of each substituent (in

alphabetical order) as a prefix to the name of the main

chain.

2-chloro-3-methylpentane

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C

H

H

C

Cl

H

C

H

CH3

CH C

H

H

H

H

H

1 2 3 4 5

Learning Check

Give the IUPAC name for the following compound:

29

C

H

Br

C

Br

H

C

CH3

H

CH

H

H

H

Solution

Give the IUPAC name for the following compound:

Step 1 Write the alkane name of the longest chain of

carbon atoms.

The longest chain has

four carbons, butane.

30

C

H

Br

C

Br

H

C

CH3

H

CH

H

H

H

C

H

Br

C

Br

H

C

CH3

H

CH

H

H

H

Solution

Step 2 Number the carbon atoms starting from the end

nearer a substituent.

Step 3 Give the location and name of each substituent (in

alphabetical order) as a prefix to the name of the main

chain.

1,2-dibromo-3-methylbutane

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C

H

Br

C

Br

H

C

CH3

H

CH

H

H

H1 2 3 4

Naming Cycloalkanes with Substituents

Give the IUPAC name for the following cycloalkane.

Step 1 Write the alkane name of the longest chain

of carbon atoms.

The longest chain is a

six-member ring, cyclohexane.

32

CH2CH3

C

C

C

C

C

C CH2CH3

Solution

Step 2 Number the carbon

atoms starting from the end

nearer a substituent.

Step 3 Give the location and name of each substituent (in

alphabetical order) as a prefix to the name of the main

chain.

For cycloalkanes with just one substituent, there is no need

to give the location of the substituent:

ethylcyclohexane

33

C

C

C

C

C

C CH2CH3

1

23

4

56

Drawing Formulas for Alkanes

34

Draw the structure for 1-chloro-1,2-dimethylheptane

heptane – 7-carbon chain

methyl group on carbon 1 and 2

chlorine on carbon 1

Guide to Drawing Formulas for Alkanes

35

Learning Check

Draw the condensed structural formula for

3-bromo-1-chlorobutane.

36

Solution

Draw the condensed structural formula for

3-bromo-1-chlorobutane.

Step 1 Draw the main chain of carbon atoms.

The longest chain in butane has four carbon atoms. CCCC

Step 2 Number chain and place the substituents on the carbons indicated by the numbers. 1 2 3 4

3-bromo: Br goes on carbon 3. CCCC Cl Br 1-chloro: Cl goes on carbon 1.

37

Cl

Br

Solution

Draw the condensed structural formula for

3-bromo-1-chlorobutane.

Step 3 Add hydrogen to complete four bonds to each carbon.

CH2CH2CHCH3

Cl Br 3-bromo-1-chlorobutane

38

Cl

Br

Learning Check

Name each of the following cycloalkanes.

A.

B.

C.

39

CH3

Cl

H2C

CH3

Solution

Name each of the following cycloalkanes.

A. methylcyclopropane

B. ethylcyclobutane

C. chlorocyclopentane

40

CH3

Cl

H2C

CH3

Some Uses of Alkanes Alkanes with one to four carbons are gases at room temperature

and are widely used as heating fuels.

methane, ethane, propane, butane

Butane has four carbons:

Alkanes with five to eight carbons are highly volatile liquids at room temperature, making them useful in fuels such as gasoline.

pentane, hexane, heptane, octane

Octane has eight carbons:

41

Alkanes with 9−17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels.

Decane has 10 carbons:

Alkanes with 18 or more carbons

• have high molar masses

• are waxy solids at room temperature

• are used in waxy coatings of fruits and vegetables

Solubility and Density of Alkanes

Alkanes are

• nonpolar

• insoluble in water

• less dense than water

• flammable in air

The crude oil in oil spills floats on top of the water,

forming a thin layer on the surface because it is less dense

than water.

42

Combustion of Alkanes

Alkanes

• have strong CC bonds

• react with oxygen gas to make carbon dioxide and

water in combustion reactions

• release energy when CC bonds are broken in

combustion reactions

CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + energy

43

Learning Check

Propane is a fuel often used in barbeques. Write a balanced

equation for the complete combustion of propane.

44

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)

45

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

46

Functional Groups

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

47

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.

48

Comparing Alkenes, Alkynes, and Aromatic

Compounds

49

Learning Check

50

Identify the following compounds as an alkene, alkyne, or

aromatic compound.

A.

B.

C.

Solution

51

Identify the following compounds as an alkene, alkyne or

aromatic compound.

A. aromatic

B. alkene

C. alkyne

Alcohols, Thiols, 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 (COC) functional group.

52

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 carbon is attached to a

hydrogen.

In a ketone, the carbon

of the carbonyl group (C=O) is

attached to two carbon atoms.

53

C

H

O

C

C

C

O

Carboxylic Acids and Esters

Carboxylic acids contain the

carboxyl group, which is a

carbonyl group attached

to a hydroxyl group.

COOH

An ester contains the

carboxyl group between

carbon atoms.

COOCH3

54

C

C

OH

O

C

C

O

O

Amines

Amines

• have a functional group that

contains a nitrogen atom

• are derivatives of ammonia,

NH3, in which one, two, or

three hydrogen atoms are

replaced with carbons

55

H3C N

H

H

H3C N

CH3

H

H3C N

CH3

CH3

Amides

Amides

• have an amine group instead

of an OH group on the

carbonyl carbon

• are an important biological

functional group, the

simplest amide

being urea

56

C

N

O

H2N

C

O

NH2

Classification of Organic Compounds

57

Learning Check

Classify each of the following as an alcohol, ether,

aldehyde, ketone, carboxylic acid, ester, amine, or amide.

A.

B.

C.

D.

E.

58

Solution

Classify each of the following as an alcohol, ether,

aldehyde, ketone, carboxylic acid, ester, amine, or amide.

A.

B.

C.

D.

E.

59

alcohol

ether

amine

carboxylic acid

ester

Concept Map – Organic Compounds

60