Chapter 11: Unsaturated Hydrocarbons

1
Chapter 11 Unsaturated Hydrocarbons

• Properties of Alkenes Alkynes
• Alkenes and Alkynes Nomenclature
• Geometric Isomers
• Principal Reactions of Alkenes
• Aromatic Hydrocarbons
• Nomenclature of Benzene Derivatives
• Properties and Uses of Aromatic Compounds

2
UNSATURATED HYDROCARBONS
Contain carbon carbon multiple bonds
CnH2n
Alkenes
CnH2n-2
Alkynes
Unsaturated Fats and Oils
Some Examples
Prostaglandins
Steroids
3
ALKENES

• The family of hydrocarbons with one or more
  double bonds between carbons.

H
H
C
C
H
H
These bonds are not identicle
4
Geometry
Alkanes - tetrahedral
Alkenes - trigonal planer
Alkynes - linear
5
Geometry
For larger carbon chains ...
multiple bonds also affect the overall geometry.
6
Physical properties

• Similar to alkanes
• Solubility
• Soluble in nonpolar solvents
• Not soluble in water
• Low density, boiling point and melting point
• Properties vary based on chain size
• Interesting physical property.
• Alkenes with several double bonds will have a
  color associated with them.

7
Colored alkenes
lycopene - red of tomato, paprika and watermelon
?-carotene, yellow of carrots and yams
8
Naming alkenes

• Very similar to rules for alkanes with the
  following changes
• All alkenes have names ending in -ene. (Example
  butene, pentene, heptene)
• The longest chain of atoms containing the double
  bond is the parent chain.

6
5
C
H
C
H
C
H
4
2
2
3
C
H
C
H
C
H
C
H
C
H
3
2
3
1
2
3
9

• Number the chain starting at the end closest to
  the first double bond.
• Indicate the position of the double bond by using
  the number of the first carbon in the double
  bond.

C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
4
3
2
1
8
7
6
5
2-pentene
10

• When there is more than one double bond in chain,
  the prefixes di, tri, etc.. Are included with the
  ene ending.

2,5-octadiene
Substituents attached to chain are named as
usual.
11
Examples

• C-C-CC-C
• \___ 2-pentene
• C-C-CC
• C
• \___
  3-methyl-1-butene
• Cl-C-C-C-C
• CC-C-C
• 
  \___5-chloro-3-octene

5
6
7
8
1
2
3
4
12
5-methyl-1-heptene
5-methyl-2-heptene
13
More examples
C - C - C C - C C
C C - C - C C - C
C - C
14
More examples
C - C - C C - C C
4-methyl-2-pentene
C C - C - C C - C
C - C
15
More examples
C - C - C C - C C
4-methyl-2-pentene
C C - C - C C - C
C - C
3-ethyl-1,4-hexadiene
16
More examples
C - C - C C - C C
4-methyl-2-pentene
C C - C - C C - C
C - C
3-ethyl-1,4-hexadiene
1
6
2
5
1,3-cyclohexadiene
3
4
17

• Name the compounds below

2-ethyl-1-butene
3
4
5
2
1
6
5-methyl-1,3-cyclohexadiene
18
Naming alkynes

• Similar to alkenes -
• longest chain must contain the triple bond.
• number carbons so the triple bond has the lowest
  possible value.
• indicate the location of the triple bond.
• change ending to -yne.

19
Naming alkynes
C C-C-C
_ _ _
Four carbons - use base of but- Contains a
triple bond so use -yne
Triple bond is between first and second carbon,
number it as 1
1-butyne
20
Additional examples
21
Additional examples
2-pentyne
22
Additional Examples
2-pentyne
4-bromo-1-butyne
23
Additional Examples
2-pentyne
4-bromo-1-butyne
1
2
3
3-ethyl-1-hexyne
5
4
6
24
Geometric isomers

• These exist when two or more arrangements are
  possible due to the type of bond.
• Alkanes - can rotate about all bonds
• no geometric isomers
• Alkenes - rigid bond
• can have geometric isomers
• Alkynes - rigid bond but linear
• no geometric isomers

25
Geometric isomers
There are two possible arrangements Example
2-butene
cis Largest groups are on the same side.
trans Largest groups are on opposite sides.
26
Retinal and sight
cis
Light causes a change from cis to trans. This
is how we see. Enzymes are used to convert
back to the cis form.
light
several steps
trans
27
3-D models of retinal
cis
trans
28
Geometric isomers

• When the structure is known, the terms cis or
  trans is included in the name.

cis-2-butene trans-2-butene
29
Geometric isomers

• General rules for determining cis or trans
  isomers of alkenes
• 1. Locate alkene bond
• 2. Determine if it is unsymetrical
• 3. If unsymetrical
• a. cis if the two large groups are on
• the same side
• b. trans if the two large groups are on
• opposite sides

30
Examples

• H3C H
• \ /
• C C
• / \
• H H
• 1-propene, no cis or
  trans
• CH3 CH3
• \ /
• C C
• / \
• Br H
• cis-2-bromo-2-butene
  

31
Is it cis or trans?
32
Examples

• H3C CH3
• \ /
• C C
• / \
• H CH2CH3
• H3C H
• \ /
• C C H
• / \ /
• H C C
• / \
• H CH3

33
Examples

• H3C CH3
• \ /
• C C trans-3-methyl-2-pentene
• / \
• H CH2CH3
• H3C H
• \ /
• C C H
• / \ /
• H C C
• / \
• H CH3

34
Examples

• H3C CH3
• \ /
• C C trans-3-methyl-2-pentene
• / \
• H CH2CH3
• H3C H
• \ /
• C C H
• / \ /
• H C C trans-2-trans-4-hexadiene
  
• / \
• H CH3

35
Reactions of alkenes

• Primarily reactions involve the double bond.
• They can react like alkanes as well.
• Major class of reaction is addition.
• - breaking the bond and adding something to
  each carbon.

R-CC-R R-C-C-R
We group
reactions by what is added.
36
Reactions of alkenes

• Hydrogenation
• Addition of a molecule of H2
• Results in the formation of an alkane

R-CC-R H2 R-C-C-R


H H
Usually requires heat, pressure and a catalyst
like Pt, Pd or Ni.
37
Reactions of alkenes

• Uses for Hydrogenation
• Alkenes have lower MP and BP than alkanes.
• Vegetable oils contain -CC- groups.

Food labels now list the amount of
saturated and unsaturated fat they contain.
Ni
Vegetable oil H2 Margarine
Heat
38
Reactions of alkenes

• Hydration
• The addition of water to an alkene.
• one carbon get an H, the other an OH
• produces an alcohol

The reaction requires a small amount of acid to
be present to work. (a catalyst)
39
Reactions of alkenes

• We can predict where the OH group will go.
• Markovnikovs Rule
• The carbon with the most hydrogens bonded to
  it initially, will receive the hydrogen.

Can you try that again? This time in English!
40
Reactions of alkenes

• Markovnikovs Rule
• Them that has, gets!
• Only used if the alkene is unsymmetrical

H H H H
H-C-CC-C-H
H H
H H H H
H-C-C-CC-H H H
symmetrical
unsymmetrical
41
Reactions of alkenes
This carbon has 2 H It gets the H
H H H H
H - C - C - C C - H
H H
This carbon has 1 H It gets the OH
42
Reactions of alkenes
H H H H
H H H H


H-C-C-CC-H H2O H-C-C-C -
C-H

H H
H H OH H
H
Always look for the carbon with the
most hydrogens. It will get the additional H.
43
Reactions of alkenes

• Hydrohalogenation
• Addition of HX to an alkene
• HX - HF, HCl, HBr, HI
• It follows Markovnikovs rule where the H ends up
  on the carbon with the most hydrogen to start
  with.

R-CC-R HX R-C-C-R


H X
44
Reaction of alkenes
H H H H
H H H H

H-C-C-CC-H HCl
H-C-C-C-C-H

H
H H H
Cl H
The halogen adds to the side with the least
hydrogen.
45
Aromatic hydrocarbons

• Best represented by benzene
• a six carbon ring
• three alternating double bonds
• electrons in bonds spread themselves out
• exists as average, resonance structure

46
Aromatic hydrocarbons
Bonds blend together. No exact double bonds.
47
Naming aromatic compounds

• The ring structure is the base name

benzene
naphthalene
anthracene
Well stick to benzene rings for naming. That
will keep us busy enough!
phenanthrene
48
Naming aromatic compounds

• Simple compounds are named as substituted benzene
  derivatives.

CH2CH3
Cl
ethylbenzene
chlorobenzene
NO2
CH2CH2CH3
nitrobenzene
propylbenzene
49
Naming aromatic compounds
Many have special names for historical reasons.
toluene benzaldehyde benzoic
acid
phenol aniline
anisole
50
Disubstituted aromatic hydrocarbons
If there are two things on the benzene ring use
Cl
Cl
o-dichlorobenzene
ortho, o-
Cl
meta, m-
m-dichlorobenzene
Cl
Cl
para, p-
p-dichlorobenzene
Cl
51
Disubstituted aromatic hydrocarbons
They can also be numbered.
1,2-dichlorobenzene
1,3-dichlorobenzene
1,4-dichlorobenzene
52
Reactions of benzene

• Formation of aryl halides
• - a substitution reaction, H is replaced with X

X
catalyst
X2
HX
Example. Production of bromobenzene
Br
Fe or FeBr3
Br2
HBr
53
Reactions of other aromatics

• If toluene is used instead of benzene, we can get
  more than one product.

(40)
Fe or FeBr3
Br2 HBr

No meta form is produced for this reaction.
(60)