Ch. 10: Alkanes
Chem 20
El Camino College
1
Organic Chemistry

More than 90% of compounds are organic
compounds.
For pronunciation of organic compound
names go to
www.merriam-webster.com/dictionary
www.howjsay.com

2
Organic Chemistry
Organic chemistry covers compounds
made of carbon and hydrogen
 Other elements, such as O, N, S and Cl
may be present

3
Organic Chemistry

Organic compounds
They are mostly covalently bonded
molecules
 Usually low melting points
 Usually low boiling points
 They are usually not soluble in water,
unless a polar group is present

4
Organic Chemistry

Inorganic compounds
They are mostly ionic compounds, some are
covalent
 Usually high melting points
 Usually high boiling points
 They are usually soluble in water.

5
ALKANES

Remember that carbon has 4 bonds and is
often tetrahedral.
Wedge formula: Solid wedge represents bond coming forward.
Broken wedge represents bond going to the back.
Ordinary line represents bond on the plane
6
Lewis Structures

Each bonding pair is represented by a
dash. Sometimes we draw long molecules
with straight lines, but actually they are not
flat
H
H
:
H
C
O
C
H
:
H
H
7
Alkanes
Alkanes are a class of hydrocarbons in
which the atoms are connected only by
single bonds.
 The general formula for open-chain alkanes
is Cn H2n+2 .

8
Alkanes










CH4 methane (1C)
CH3CH3 ethane (2C)
CH3CH2CH3 propane (3C)
CH3CH2CH2CH3 butane (4C)
CH3CH2CH2CH2CH3 pentane (5C)
CH3CH2CH2CH2CH2CH3 hexane (6C)
CH3CH2CH2CH2CH2CH2CH3 heptane (7C)
CH3CH2CH2CH2CH2CH2CH2CH3 octane (8C)
CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane (9C)
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 decane (10C)
9
Drawing Formulas
In expanded formulas, every bond is shown
 In condensed formulas, carbons are shown
with the correct number of hydrogen atoms,
but not every bond is shown
 In alkane, C will always have 4 bonds, H
will always have 1 bond

10
Drawing Formulas
expanded
condensed
H
H3C
H
H
C
C
H
H
CH2
H
H3C
H
H
C
C
H
H
CH2
or
H3CH2C
11
Drawing Formulas

Hexane has six carbons. Draw expanded
and condensed formulas for hexane. (Note:
make sure every carbon has 4 bonds)
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
CH2
CH2
CH2
CH2
H3C
CH3
H
12
Drawing Formulas
Note--the chains in formulas may not be
shown as a straight line.
 Ex. What compounds are these?

H3C
H3C
H3C
CH2
CH2
CH2
H2C
CH2
H3C
CH2
CH2
butane
heptane
13
Skeletal (Geometric)Formula
(Stick structure)
Skeletal formulas contain zigzag lines
 Every corner and every end represents a
carbon
 H atoms are filled in mentally
 Butane:

Hexane
14
Structural Isomers
Isomers have the same chemical formula,
but atoms are attached differently
 2 different isomers have different properties
 Are these isomers, or the same molecule?

or
or
isomers
same molecule
15
Stereoisomers
In stereoismers atoms are attached to each
other in the same way
 But they are different in the way atoms are
oriented in space
 Chiral center is a carbon atom to which 4
different groups are attached.

16
Fisher projection



A cross represents a chiral center.
Vertical lines represent bonds going away to the back
Horizontal lines represent bond coming forward
17
Cycloalkanes
Cycloalkanes have the carbons connected
in a “ring”
 Use cyclo in the name
CH
 Ex. Condensed formula
H C
CH
for cyclohexane H C
CH

2
2
2
2
2
CH2
Draw a geometric formula for cyclopropane.
What is the chemical formula?
C 3H 6
18
Substituents
Alkanes can have attachments
 Common attachment names:

•
•
•
•
•
CH3CH3CH2CH3CH2CH2F-, Cl-, Br-, I-
methyl
ethyl
propyl
fluoro, chloro, bromo, iodo
H3C
HC
isopropyl
H3C
19
Alkanes with Substituents

1. Write the name of the longest continuous
HC
CH
CH
carbon chain
3
2
2
HC
CH3
CH3

The longest chain has 5 carbons: pentane
H 3C
CH2
CH2
HC
CH3
CH3
20
Alkanes with Substituents

2. Number the carbon chain from the end
nearer a substituent
5
4
3
H3C
CH2
CH2
2 HC
1

CH3
CH3
3. Give the location and name of the
substituent. Use a hyphen after the number
2-methylpentane
21
Alkanes with Substituents

Name these
Cl
Cl
2-chloropentane
3-chloropentane
22
Alkanes with Substituents

Name these
Br
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
CH2
H
H
H3C
2-bromopropane
3-methylheptane
23
Alkanes with Substituents

Name these, write the formula
Br
4-ethylnonane
1-bromohexane
C11H24
C6H13Br
3-methylnonane
C10H22
24
Alkanes with Substituents

Draw the skeletal formula
2-bromobutane
1-chlorodecane
Br
Cl

Draw the expanded formula
1-iodopropane
H
I
H
H
C
C
C
H
H
H
cyclobutane
H
H
H
H
C
C
H
H
C
C
H
H
H
25
Alkanes with Substituents

Name these, write the formula
F
2-fluorohexane
cyclopentane
C6H13F
C5H10
4-propylheptane
C10H22
26
Alkanes with Substituents

4. Name substituents in alphabetical order
H

H
H
H
H
Br
I
C
C
C
C
C
C
H
H
H
H
H
H
Name this
H
2-bromo-1-iodohexane
CH3
Br
3-bromo-2-methylpentane
27
Alkanes with Substituents

Name these
Cl
Cl
F
Br
F
Br
1-bromo-2-chlorobutane
2-chloro-1-fluorobutane
1-bromo-1-fluoro-2-methylpropane
28
5. Use prefixes like di-, tri-, tetra- for more
than one copy of a substituent
 Every substituent must have its own
number
 Prefixes are not part of alphabetical order.

H
H
CH3
CH3
H
C
C
C
C
H
H
H
H
Br
H
2,3-dimethylbutane
Br
Cl
Cl
Cl
2,2-dibromobutane
1,2,2-trichlorobutane
30
Br
Br
H
Br
CH3
H
C
C
C
C
H
H
H
H
H
Br
CH3
C
C
CH
H
H
H
1,2-dibromo-3-methylbutane
H
1,2-dibromobutane
F
3-bromo-2-fluoropentane
Br
32

7. When a single substituent is attached to
a cycloalkane, no number is needed.
Cl
chlorocyclohexane
Write the name and chemical formula:
ethylcyclobutane
C6H12
33
Draw these
CH3
ethane H3C
 2-methylpropane

Br

bromocyclopentane

1,4-dichloro-2-methylbutane
CH3
Cl
Cl
Br

1,1,2,3-tetrabromopropane
Br
Br
Br
34
Properties, Uses
Alkanes are nonpolar, so they’re insoluble in water
 Alkanes are less dense than water (they float on
water)
 Common alkanes: methane (natural gas), propane
(bbq fuel), butane (lighter fuel), octane (fuel)
 Alkane mixtures also form gasoline, mineral oil,
and vaseline.

35
Combustion
The burning of methane in a Bunsen burner is
an example of combustion of an alkane
 alkane + O2  CO2 + H2O + energy
 Write a balanced equation for the combustion
of methane gas

CH4
_____(g)
+ 2 O2(g) 
CO2(g) + 2 H2O(g)
36
Compound Types
Alkenes (contain C=C)
 Alkynes (contain CC)
 Alcohols (contain -OH)
 Ethers (contain C-O-C)
 Aldehydes (contain H-C=O)
 Ketones (contain C=O)
 Carboxylic acids (contain HO-C=O)
 Esters (contain RO-C=O)
 Amines (contain N).

37
38
39
40
41
42
43
44
45
46
What is the compoud type?
O
alkene
H3C
ketone
C
H3C
CH3
N
H
OCH3
carboxylic acid
amine
OH
O
CH3
H3C
O
C
O
H 3C
ester
C
H 3C
aldehyde
H
alkane
47
Substitution Reactions
Your next organic reactions will be on
haloalkanes (alkanes with a halogen atom
substituent)
 In substitution reactions, one halogen will be
substituted for another halogen
 CH3Br + Cl  CH3Cl + Br

48
Draw Products, Name the
Organic Product
H3C
CH2Br
+ Cl -
H3C
CH2Cl
+ Br
chloroethane
49
-
Draw Products, Name the
Organic Product
CH3
CH3
H3C
C
CH3
I
-
+ Cl
H3C
C
+ I-
Cl
CH3
2-chloro-2-methylpropane
50
Name These
Br
Br
Br
bromoethane
Br
Br
Br
Br
Br
Br
bromoethane
1,1-dibromoethane
1,2-dibromoethane
1,1,2-tribromoethane
51
Name These
Br
Br
Br
Br
Br
Br
Br
Br
2-bromopropane
2-bromo-2-methylpropane
1,2-dibromo-2-methylpropane
1,1,1,2-tetrabromo-2-methylpropane
52
Draw Products, Name the
Organic Product
Br
Cl
-
+ Cl
+ Br
bromocyclohexane
53
-