Power Point to Accompany
Principles and Applications of
Inorganic, Organic, and
Biological
Chemistry
Denniston, Topping, and Caret
th
4 ed 12
Chapter
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
12-1
12.1 Alkenes and Alkynes
Alkenes have one or more carbon-carbon
double bonds.
Alkynes have one or more carbon-carbon
triple bonds.
Simplest alkene: ethene (ethylene) C2H4
Simplest alkyne: ethyne (acetylene) C2H2
H
H
C C
H C C H
bond angles
H
H
o
180
bond angles
approximately 120o
Alkenes and Alkynes
Physical properties of the alkenes and
alkynes mirror those of alkanes. They
are nonpolar and consequently are not
soluble in water but highly soluble in
nonpolar solvents.
Boiling points rise with molecular
weight.
12-3
12.2 IUPAC Names
Base name from longest chain
containing the multiple bond.
Change -ane to -ene or -yne.
Number from the end that will give the
first carbon of the multiple bond the
lower number.
Prefix the name with the number of the
first multiple bond carbon.
Prefix branch/substituent names as for
alkanes.
IUPAC Names-2
CH3
CH2 CH3
CH3 CH CH2 CH C
3-ethyl-6-methyl-3-heptene CH2 CH3
Name
Name
CH3CH C
Br
2-bromo-3-hexyne
C CH2CH3
Names-3
Cyclic alkenes are named like cyclic
alkanes. Prefix name with cyclo.
Numbering must start at one end of the
double bond and go through the bond.
Substituents must have the lower
possible numbers.
CH
Name:
Cl
CH
CH2
CH2
3
CH
CH
CH
5-chloro-3-methylcyclohexene
12.3 Geometric Isomers, The pi Bond
Two p orbitals overlap side-by-side
C  C
C
C
pi bond has two lobes
sigma bond between carbons
Geometric Isomers-cont.
2-butene is the first example of an
alkene which can have two different
structures - based on restricted rotation
about the double bond.
CH3
CH3 CH3
C C
C C
H
H
CH3
H
H
trans-2-butene
cis-2-butene
Identifying cis/trans Isomers
If one end of the C=C has two groups
the same, cis/trans isomers (geometric
isomers) are not possible.
Both carbons of the C=C must have two
different groups attached.
Find a group common to both ends of
the C=C.
If the common group is on the same
side of the pi bond, the molecule is
cis; if on the opposite side , the
molecule is trans.
Identifying cis/trans Isomers-2
The common group (at each end) is the
methyl group.
Both CH3s are on the same side of the pi
bond.
cis-3-methyl-2-pentene
CH3
C
H
CH3 Neither ene carbon
C
has two groups the
same.
CH2 CH3
Identifying cis/trans Isomers-3
The common group is the chlorine atom.
The chlorines are on opposite sides of
the pi bond.
trans-1,2-dichloro-1-butene
Cl
CH2 CH3
C C
H
Cl
Quiz: cis/trans Isomers
Decide whether each compound is cis, trans,
or neither. Click to see the answers.
A: methyls are trans
B: No c/t. Right C has two isopropyls.
C: hydrogens are cis
CH3
CH3
CH3
Cl
CH CH3 CH3 CH2
CH2 CH3
CH3
CH
B
C C
C C
C C
A
CH CH3
H
H C
H
CH3
CH3
CH3
12.4 Alkenes in Nature
Alkenes are abundant in nature.
Ethene is a fruit ripener and promotes
plant growth.
Polyenes built from the isoprene
skeleton are called isoprenoids.
The next slide shows some isoprenoids.
CH3
CH2 C CH CH2
12-13
Isoprenoids
CH3
CH3
C CH CH2CH2 C CH CH2OH
CH3 Geraniol (rose and geraniums)
Limonene (oil of
lemon and orange)
CH3
C
H2C
CH
H2C H CH2
C
C
H3C
CH2
CH3
CH3
CH2OH
C
C
CH2
CH2 CH
CH2 CH
CH2
CH C
CH3
CH3
Farnesol (Lily of the Valley)
12-14
12.5 Alkene Reactions
There are two kinds of reactions typical
of alkenes:
Addition: two molecules combine to
give one new molecule.
Redox: oxidation and reduction
The two classes are not always mutually
exclusive.
12-15
Addition: General
CH3 CH CH CH3
+ AQ
CH3 CH CH CH3
A
Q
A small molecule, AQ, reacts with the pi
electrons of the double bond.
The pi bond breaks and its electrons are
used to bond to the A and Q pieces.
Some additions require a catalyst.
12-16
Reagents Adding to Alkenes
1. Symmetrical reagents:
H2 (Pt, Pd, or Ni as catalyst)
Br2, Cl2
2. Unsymmetrical reagents (acids)
HCl, HBr
H2O (requires strong acid catalyst
eg. H3O+, H2SO4, H3PO4)
3. Self addition or polymerization.
12-17
Symmetrical Reagents: Example
CH3 CH CH2
H2, Pt
H H
CH3 CH CH2
or
CH3 CH2 CH3
Note: the two hydrogens attach to each
end of the double bond. There is no
double bond in the product! The
reaction is called hydrogenation.
12-18
Unsymmetrical Reagents: Example
OH
H2O, H+ CH3 CH
CH3 CH CH2
H
CH3 CH
H
CH2
OH
CH2
Two products are possible
depending how the reagent (as H
and OH) adds to the ends of the pi
bond.
12-19
Markovnikov’s Rule
Dimitri Markovnikov (Russian)
observed many acid additions
to C=C systems. He noticed
that in all cases, the majority of
the hydrogen went to a specific
end of the double bond. He
formulated his rule:
12-20
Markovnikov’s Rule-2
When an acid (H-OH, H-Cl,
H-Br) adds to a double bond,
the H of the acid usually
goes to the end of the double
bond with more hydrogens
attached initially.
12-21
Major product: HCl + propene
CH3 CH2 CH2 Cl
CH3CH CH2
+ HCl
minor prdt.
Cl
CH3 CH CH3
major prdt.
H goes to carbon with
more hydrogens
12-22
Addition Polymers
Alkene molecules add “head to tail”
using heat, pressure, and a catalyst.
General
R R R R R R R R
R R
nC C
C C C C C C C C
etc.
R R R R R R R R
R R
R R
C Cn
R R
*
*
12-23
Addition Polymers: Examples
Monomer
Polymer
Name
Polystyrene
CH2 CH
* CH2 CH n*
PolymethylCH3
CH3
methacrylate
CH2 C
* CH2 C n *
Lucite
O C O CH3
O C O CH3
PolytetraCF2 CF2
* CF2 CF2 n* fluoroethylene
Teflon
Cl
Cl
Polyvinyl
CH2 CH
* CH2 CH n * Chloride (PVC)
12-24
Alkenes: Reduction
Alkenes add two hydrogens to give
alkanes. We have already seen this
reaction under symmetrical additions.
Eg:
CH3 CH CH2
H2, Pt
H H
CH3 CH CH2
or
CH3 CH2 CH3
12-25
12.5 Aromatic Hydrocarbons
Benzene’s structure was first proposed
by Kekule in the 1850s. He proposed a
cyclic structure for benzene, C6H6.
Kekule realized that there was
something special about benzene
because, although his structures
showed double bonds, the molecule
did not react as if it had any
unsaturation.
12-26
History-2
The two equivalent structures proposed
by Kekule are recognized today as
resonance structures. The real
benzene molecule is a hybrid with each
resonance structure contributing to the
true structure.
H
HC
HC
H
C
C
H
CH
HC
CH
HC
C
C
H
CH
CH
12-27
Bonding in Benzene-Modern
2
The carbons in benzene are sp
2
hybridized. Two sp orbitals are
used to bond to other carbons and
one to bond to hydrogen. The ring
and all the hydrogens are coplanar.
This describes the sigma bonding
in the ring. (Picture on next slide.)
12-28
Sigma network on benzene
set of 3 sp2
hybrid orbitals
on a carbon
H
H
H
C at center
of set
sp2-sp2
overlap
H
H
H
12-29
Pi bonding on benzene
The six p orbitals unused for the sp2
hybrids are perpendicular to the plane
of the benzene ring. They overlap with
one another to form the pi cloud, a ring
of electrons above and below the ring.
The pi cloud electrons are free to move
around the ring. They are said to be
delocalized.
The next slide shows pi cloud formation.
12-30
Pi Cloud Formation in Benzene
Insert Fig 12.7 to fill space
The current model of the bonding in benzene.
12-31
Magenta lines=pi overlap
IUPAC Names: Benzenes
Certain groups change the base name of
the ring system. E. g.
CH3
Toluene
OH
Phenol
NH2
Aniline
COOH
Benzoic
acid
12-32
IUPAC Names: Benzenes
For monosubstituted benzenes, name
the group and add “benzene” (unless
the group conveys a special name.)
Name:
NO2
Cl
CH2 CH3
nitrobenzene
chlorobenzene
ethylbenzene
12-33
IUPAC Names: Benzenes-2
For disubstituted benzenes, name the
groups in alphabetical order. The first
named group is at position 1.
If a “special group” is present, it must be
number 1 on the ring.
An older system of naming uses ortho
(o), meta (m), and para (p) to indicate
groups that are 1,2, 1,3 and 1,4 on the
ring.
12-34
IUPAC Names: Benzenes-3
Name:
CH3
CH2 CH3
Br
NO2
1-bromo-2-ethylbenzene
o-bromoethylbenzene
Cl
3-nitrotoluene
m-nitrotoluene
Cl
1,4-dichlorobenzene or p-dichlorobenzene
12-35
IUPAC Names: Benzenes-4
A final note:
When the benzene ring is a substituent
on a chain (C6H5), it is called a phenyl
group. Note the difference between
phenyl and phenol (a functional group).
CH2 CH CH2
CH CH3
4-phenyl-1-pentene
12-36
Reactions of Benzene
Benzene undergos aromatic substitution
reactions: an atom or group
substitutes for an H on the ring.
All benzene reactions (in our class)
require a catalyst.
The reactions are:
1. Nitration
2. Halogenation
3. Sulfonation
12-37
Reactions of Benzene-1
Nitration places the nitro group on the
ring. Sulfuric acid is needed as a
catalyst.
O
+
HNO3
H2SO4
N O
+ H2O
12-38
Reactions of Benzene-2
Halogenation places a Br or Cl on the
ring. Fe or FeCl3 are used as catalysts.
Cl
+
Cl2
Fe
bromine may substitute for chlorine
12-39
Reactions of Benzene-3
Sulfonation places an SO3H group on
the ring.
O
conc.
+ SO3
H2SO4
S OH
O
+ H2O
12-40
Heterocyclic Aromatics
Rings with a hetero atom (typically O, N,
S) and delocalized electrons are also
aromatic. Many have a six membered
ring, some have a five membered ring.
Eg:
N
S
O
N
N
pyridine pyrimidine furan thiophene
12-41
Heterocyclic Aromatics-cont.
Heterocyclic aromatics are similar to
benzene in stability.
Many are significant biologically.
N
N
N
N
pyrimidine purine
H
N
pyrrole
N
N
Found in
DNA and RNA
H
Found in hemoglobin
and chlorophyll
12-42
THE END
Unsaturated
Hydrocarbons
12-43