Alkanes - Quynh Nguyen
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Transcript Alkanes - Quynh Nguyen
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
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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
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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 CC)
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
-