Chemistry 121(01) Summer 2013
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: upali@chem.latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MTWTF 8:00 am - 10:00 am; by e-mail
June 14, 2013 Test 1 (Chapters 12-13)
July 8, 2013 Test 2 (Chapters 14,15 & 16)
July 19, 2013 Test 3(Chapters 17, 18 & 19)
August 5, 2013 Test 4 (Chapters 20, 21 & 22)
August 8, 2013
Comprehensive Make Up Exam:
Chemistry 121, Summer 2013, LA Tech
13-1
Chapter 13: Unsaturated Hydrocarbons
Sections 4.1-4.5
Chemistry 121, Summer 2013, LA Tech
13-2
Chapter 13: Unsaturated Hydrocarbons
13.2 Characteristics of Alkenes and Cycloalkenes
13.3 Names for Alkenes and Cycloalkenes
13.4 Line-Angle Formulas for Alkenes
13.5 Isomerism in Alkenes
13.6 Naturally Occurring Alkenes
13.7 Physical Properties of Alkenes
13.8 Chemical Reactions of Alkenes
13.9 Polymerization of Alkenes: Addition Polymers
13.10 Alkynes
13.11 Aromatic Hydrocarbons
13.12 Names for Aromatic Hydrocarbons
13.13 Aromatic Hydrocarbons: Physical Properties and Sources
13.14 Chemical Reactions of Aromatic Hydrocarbons
13.15 Fused-Ring Aromatic Compounds
Chemical Connections: Ethene: A Plant Hormone and High-Volume
Industrial Chemical; Cis-Trans Isomerism and Vision; Carotenoids: A
Source of Color; Fused-Ring Aromatic Hydrocarbons and Cancer
Chemistry 121, Summer 2013, LA Tech
13-3
IUPAC Nomenclature of Alkyne
 CAG 13.2
Chemistry 121, Summer 2013, LA Tech
13-4
Unsaturated Hydrocarbons cont’d
→ Fig. 13.18
2-chlorotoluene
molecule
Chemistry 121, Summer 2013, LA Tech
Copyright © Houghton Mifflin Company. All rights reserved.
13-5
13 | 5
Unsaturated hydrocabons
Hydrocarbons with carbon-carbon double bonds
and triple bonds
double bonds: alkenes
triple bonds: alkynes
three alternating double bond in 6 carbon ring:
aromatics
Chemistry 121, Summer 2013, LA Tech
13-6
Unsaturated Hydrocarbons in Use
Beta-carotene is in carrots
Ethene is the hormone
that causes tomatoes to ripen.
Chemistry 121, Summer 2013, LA Tech
Acetylene: Welding
sex pheromones in insect control
involves luring insect into a trap.
13-7
Unsaturated Hydrocarbons:
Alkenes
Alkynes
H
Arenes
H
H
C
C
C
C
C
C
H
H
H
ethene
C2H4
ethyne
C2H2
CnH2n
unsaturated
alkene
Chapters 13
CnH2n-2
unsaturated
alkyne
Chapters 13
Chemistry 121, Summer 2013, LA Tech
benzene
C6H6
CnHn
Aromatic
Arene
Chapter 13
13-8
Units of Unsaturation
Compounds that have have fewer hydrogens than
saturated hydrocarbons (CnH2n+2). Two hydrogen are
considered as unit of unstauration
Cycloalkane ring
CnH2n (one unit of unsat.)
Unsaturated hydrocarbons:
bond
CnH2n (one unit of unsat.)
bond
CnH2n-2 (two units of unsat.)
Chemistry 121, Summer 2013, LA Tech
13-9
Structure of Alkenes
• Alkene: contains a carbon-carbon double bond and has
the general formula CnH2n
• The two carbon atoms of a double bond and the four
atoms bonded to them lie in a plane, with bond angles
of approximately 120°
H
121.7°
H
124.7°
H
C C
H
CH 3
C C
H
Ethylene
Chemistry 121, Summer 2013, LA Tech
H
H
Propene
13-10
Bonding in ethene (ethylene)
→ Fig. 13.1 In ethene, the atoms are in a flat rather than a tetrahedral
arrangement.
Chemistry 121, Summer 2013, LA Tech
13-11
Planar Structure of Alkenes
According to the orbital overlap model, a double bond
consists of
•
•
a s bond formed by overlap of sp2 hybrid orbitals
a p bond formed by overlap of parallel 2p orbital
Rotating by 90°breaks the pi bond
Chemistry 121, Summer 2013, LA Tech
13-12
Structure of Alkynes
The functional group of an alkyne is a carbon-carbon triple
bond
A triple bond consists of
• one s bond formed by the overlap of sp hybrid orbitals
• two p bonds formed by the overlap of sets of parallel 2p
orbitals
Chemistry 121, Summer 2013, LA Tech
13-13
Alkenes
Second members of the hydrocarbon family.
• contain only hydrogen and carbon
• have single bonds and at least one C=C double
bond
All members have the general formula of
CnH2n
Twice as many hydrogen
as carbon
Chemistry 121, Summer 2013, LA Tech
13-14
Alkenes: Naming and Structures
One simple class of compound is the alkene
which has only C, H and single bonds.
• ethene
• C2H4
• CH2CH2
Chemistry 121, Summer 2013, LA Tech
propene
C3H6
CH3CH2CH2
2- butene
C4H8
CH3CH2CHCH3
13-15
IUPAC Nomenclature of Alkenes and Alkynes
• name the longest continuous carbon chain containing the
multiple bond(s) (parent chain). If cyclic, ring is the parent.
• use the infix -en- to show the presence of a carbon-carbon
double bond
• use the infix -yn- to show the presence of a carbon-carbon
triple bond
• number the parent chain to give the 1st carbon of the
double/triple bond the lower number
• If both double and triple are present and cannot have the
same #, then double bonds take priority.
• follow IUPAC general rules for numbering and naming
substituents
• for a cycloalkene, the double bond must be numbered 1,2
Chemistry 121, Summer 2013, LA Tech
13-16
IUPAC Nomenclature of Alkynes
• use the infix -yn- to show the presence of a carboncarbon triple bond
• number the parent chain to give the 1st carbon of the
triple bond the lower number
• follow IUPAC rules for numbering and naming
substituents
2
4
1
3
3-Methyl-1-bu tyne
Chemistry 121, Summer 2013, LA Tech
1
2 3
4
5
6
7
6,6-D imethyl-3-heptyne
13-17
Example of IUPAC Nomenclature of Alkenes
Cycloalkanes
6
5
4
6
2
3
1
1-Hexen e
5
5
4
3
2
4
3
1
2
1
4-Meth yl-1-h exene
2-Ethyl-3-methyl1-p entene
2
4
3
5
CH3
3
4
1
2
3-Methylcyclopenten e
Chemistry 121, Summer 2013, LA Tech
5
1 CH 3
6 CH 3
1,6-D imeth ylcycloh exene
13-18
Nomenclature of Alkenes: Common Names
Some alkenes, particularly low-molecular-weight ones, are
known almost exclusively by their common names
CH3
IUPA C:
Common:
CH2 =CH2
CH3 CH=CH2
CH3 C=CH2
Ethene
Ethylene
Propene
Propylene
2-Methylprop ene
Isobutylene
Chemistry 121, Summer 2013, LA Tech
13-19
Alkenes
First four members of the alkanes
Name
# of C
Condensed formula
Ethene
2
CH2=CH2
Propene
3
CH3CH=CH2
2-Butene 4
CH3CH=CHCH3
Called a homologous series
• “Members differ by number of CH2 groups”
Chemistry 121, Summer 2013, LA Tech
13-20
Physical State of Alkynes
Physical state summary for unbranched 1 alkynes at room
temperature and pressure.
Chemistry 121, Summer 2013, LA Tech
13-21
Cis and trans Geometrical isomers of alkenes
two groups are said to be located cis to each other if they
lie on the same side of a plane with respect to the double
bond.
If they are on opposite sides, their relative position is
described as trans.
Chemistry 121, Summer 2013, LA Tech
13-22
Isomerism in Alkanes & Alkenes
Fig. 13.2 A comparison of structural isomerism possibilities for
four and five-carbon alkane and alkene systems.
Chemistry 121, Summer 2013, LA Tech
13-23
Cis-trans isomerism in 2-butene
← Fig. 13.3 Cis-trans isomers: Different representatives of the cis
and trans isomers of 2-butene.
Chemistry 121, Summer 2013, LA Tech
13-24
Unsaturated Aromatic Hydrocarbons
 CC 13.2
Chemistry 121, Summer 2013, LA Tech
13-25
Geometrical Stereoisomerism
Because of restricted rotation about a C-C double bond,
groups on adjacent carbons are either cis or trans to
each other
H
H
C
H3 C
C
CH3
C
CH3
cis-2-Buten e
mp -139°C, bp 4°C
Chemistry 121, Summer 2013, LA Tech
H
H3 C
C
H
t rans-2-Buten e
mp -106°C, bp 1°C
13-26
Physical Properties
Alkenes and alkynes are nonpolar compounds
• the only attractive forces between their molecules are
dispersion forces
Their physical properties are similar to those of
alkanes of similar carbon skeletons
• those that are liquid at room temperature are less dense
than water (1.0 g/m L)
• they dissolve in each other and in nonpolar organic
solvents
• they are insoluble in water
Chemistry 121, Summer 2013, LA Tech
13-27
Cis-Trans Isomerism
• trans alkenes are more stable than cis alkenes because
of nonbonded interaction strain between alkyl
substituents of the same side of the double bond
Chemistry 121, Summer 2013, LA Tech
13-28
Summary of Physical State of Unsaturated
Hydrocarbons
Chemistry 121, Summer 2013, LA Tech
13-29
Geometric isomers
There are two possible arrangements.
Example 2-butene
CH3
H3 C
C=C
C=C
H
H
cis
Largest groups are
on the same side.
Chemistry 121, Summer 2013, LA Tech
H
H3 C
H
CH3
trans
Largest groups are
on opposite sides.
13-30
Cis-Trans Isomerism in Cycloalkenes
• the configuration of the double bond in cyclopropene through
cycloheptene must be cis; these rings are not large enough to
accommodate a trans double bond
H
CH3
C H3
H
• cyclooctene is the smallest cycloalkene that can accommodate a
trans double bond
t ra ns- Cy clo octene
Chemistry 121, Summer 2013, LA Tech
ci s-Cycl oo ctene
13-31
Cis-Trans Isomerism
Dienes, trienes, and polyenes
• for an alkene with n carbon-carbon double bonds, each
of which can show cis-trans isomerism, 2n cis-trans
isomers are possible
• consider 2,4-heptadiene; it has four cis-trans isomers,
two of which are drawn here
Doub le bond
C2 -C3 C4 -C5
trans
trans
cis
cis
trans
cis
trans
cis
Chemistry 121, Summer 2013, LA Tech
2
2
4
t rans,t rans-2,4h eptadiene
4
trans ,cis-2,4h eptadiene
13-32
Naturally Occurring
AlkenesCis-Trans Isomerism
• vitamin A has five double bonds
• four of the five can show cis-trans isomerism
• vitamin A is the all-trans isomer
OH
Vitamin A (retinol)
enzymecatalyzed
oxidation
O
H
Vitamin A aldeh yd e (retinal)
Chemistry 121, Summer 2013, LA Tech
13-33
Naturally Occurring Alkenes: The Terpenes
Terpene: a compound whose carbon skeleton can be
divided into two or more units identical with the carbon
skeleton of isoprene
head
1
2
4
tail
3
2-Methyl-1,3-b utadiene
(Is oprene)
Chemistry 121, Summer 2013, LA Tech
13-34
Terpenes with isoprene units
Chemistry 121, Summer 2013, LA Tech
13-35
Terpenes: Polymers of Isoprene
• myrcene, C10H16, a
component of bayberry
wax and oils of bay and
verbena
• menthol, from
peppermint
OH
Chemistry 121, Summer 2013, LA Tech
13-36
Terpenes
Vitamin A (retinol)
• the four isoprene units in vitamin A are shown in red
• they are linked head to tail, and cross linked at one
point (the blue bond) to give the six-membered ring
OH
Chemistry 121, Summer 2013, LA Tech
13-37
Reactions of Unsaturated Hydrocarbons
CAG 13.1
Chemistry 121, Summer 2013, LA Tech
13-38
Reactions of alkenes
Combustion
C2H4 + 4 O2
2 CO2 + 2 H2O + heat
Alkynes also under go combustion reactions
similarly
Chemistry 121, Summer 2013, LA Tech
13-39
Addition Reactions
The exposed electrons of double bonds make
alkenes more reactive than alkanes and
show addition reactions.
Chemistry 121, Summer 2013, LA Tech
13-40
Addition Reaction of Alkenes
In an alkene addition, reaction, the atoms provided by an
incoming molecule are attached to the carbon atoms originally
joined by a double bond. In the process, the double bond
becomes a single bond.
Chemistry 121, Summer 2013, LA Tech
13-41
Addition of Bromines
→ Fig. 13.9
A bromine in water
solution is reddish
brown. When a small
amount of such a
solution is added to
an unsaturated
hydrocarbon, the
added solution is
decolorized.
Chemistry 121, Summer 2013, LA Tech
13-42
Markovnikov’s Rule
Vladimir Markovnikov synthesized
rings containing four carbon atoms
and seven carbon atoms.
Chemistry 121, Summer 2013, LA Tech
13-43
Markovnikov Rule
Non symmetric alkene
In hydrohalogenation and hydration reations
hydrogen adds to the double-bonded carbon with
the most hydrogens
Chemistry 121, Summer 2013, LA Tech
13-44
Addition Polymerizations
Preparation of
polystyrene.
Chemistry 121, Summer 2013, LA Tech
13-45
Polymers of Unsaturated Hydrocarbons
(a) polyethylene (b) polypropylene (c) poly (vinyl chloride)
Chemistry 121, Summer 2013, LA Tech
13-46
Chemistry 121, Summer 2013, LA Tech
13-47
Halogenation
Halogenation - Addition of halogen to the
double bond. Textbook page xx.
Chemistry 121, Summer 2013, LA Tech
13-48
Chemistry 121, Summer 2013, LA Tech
13-49
Hydrogenation
Addition of hydrogen to the double bond. Textbook
page 84
Chemistry 121, Summer 2013, LA Tech
13-50
Chemistry 121, Summer 2013, LA Tech
13-51
Hydration
Addition of water to the double bond.
Textbook page86.
Chemistry 121, Summer 2013, LA Tech
13-52
Chemistry 121, Summer 2013, LA Tech
13-53
Polymerization
Formula
Name
Polypropylene
Monomer
CH3CH=CH2
Polymer
( CH-CH2 )
|
CH3
Polystyrene
-CH=CH2
Polychloroprene H2C=CHC=CH2
|
Chemistry 121, Summer 2013, LA Tech
Cl
( CH-CH2 )
( CH2CH=CCH2 )
|
Cl 13-54
Chemistry 121, Summer 2013, LA Tech
13-55
Chemistry 121, Summer 2013, LA Tech
13-56
Naming alkenes and alkynes
Find the longest carbon chain. Use as base
name with an ene or yne ending.
Number the chain to give lowest number for the
carbons of the double or triple bond.
Locate any branches on chain. Use base names with a
yl ending.
For multiple branch of the same type, modify name with
di, tri, ...
Show the location of each branch with numbers.
List multiple branches alphabetically
the di, tri, ... don’t count..
Chemistry 121, Summer 2013, LA Tech
13-57
Alkyne Bonding
Ethyne, is the simplest alkyne.
Chemistry 121, Summer 2013, LA Tech
13-58
Reactions of alkynes
Alkynes undergo hydration, halogenation, and
hydrohalogenation just like alkenes.
A special application is the carbide lamp (oxidation of
alkyne).
2 C (coke) + CaO (lime) + heat
---> CaC2 (calcium carbide) + CO
CaC2 + H2O
---> H-CC-H (acetylene) + Ca(OH)2
Acetylene serves as combustion fuel for the carbide
lamp.
Chemistry 121, Summer 2013, LA Tech
13-59
Aromatic hydrocarbons
Aromatic hydrocarbons - organic compounds that had
aromas and had different chemical properties from alkane
Benzene is the parent compound for the aromatic
hydrocarbons. Textbook, page90.
Consider benzene. C6H6
Chemistry 121, Summer 2013, LA Tech
13-60
Unsaturated Hydrocarbons cont’d
→ Fig. 13.17
Space-filling and
ball-and-stick
models for the
structure of
benzene.
Chemistry 121, Summer 2013, LA Tech
Copyright © Houghton Mifflin Company. All rights reserved.
13-61
13 | 61
Unsaturated Hydrocarbons cont’d
→ CC 13. 4
Chemistry 121, Summer 2013, LA Tech
13-62
Resonance Structures of Benzene
Resonance structures or contributing
structures = when two or more structure can
be drawn for a compound.
In thiscase, the real structure is something
between the proposed structures. Textbook,
page 90-91.
Chemistry 121, Summer 2013, LA Tech
13-63
Naming Aromatic Hydroarbons.
Monosubstituted benzenes:
Ar-CH2CH3 ethylbenzene
Ar-CH2-CH2-CH2-CH3 butylbenzene
Ar-CH3 (methylbenzene) toluene
Ar-X (halobenzene) bromobenzene,
Ar-NO2 nitrobenzene
Ar-SO3H benzenesulfonic acid
Ar-NH2 a nitrile substituent
Chemistry 121, Summer 2013, LA Tech
X
13-64
Nomenclature
Disubstituted benzenes
• locate substituents by numbering or
• use the locators ortho (1,2-), meta (1,3-), and para (1,4-)
Where one group imparts a special name, name the
compound as a derivative of that molecule
CH3
NH2
COOH
NO2
Cl
Br
4-Bromotolu ene
3-Ch loroaniline
2-N itroben zoic acid
(p-Bromotoluen e) (m-Ch loroaniline) (o-N itrob enzoic acid)
Chemistry 121, Summer 2013, LA Tech
13-65
Nomenclature
Polysubstituted benzenes
• with three or more substituents, number the atoms of
the ring
• if one group imparts a special name, it becomes the
parent name
• if no group imparts a special name, number to give the
smallest set of numbers, and then list alphabetically
6
1
5
2
NO2
OH
CH3
NO2
3
4
Cl
4-Ch loro-2-nitrotoluen e
Chemistry 121, Summer 2013, LA Tech
Br
6
1
5
Br
2
3
4
Br
2,4,6-Trib romophen ol
4
5
3
2
6
Br
CH2 CH3
2-Bromo-1-eth yl-4nitrob enzene
13-66
1
Chemistry 121, Summer 2013, LA Tech
13-67
Disubstituted benzenes:
Textbook, page 352.
2,6-dibromotoluene
p-diethylbenzene
3,5-dinitrotoluene
p-cholonitrobenzene
o-nitrobenzenesulfonic acid
4-benzyl-1-octene
m-cyanotoluene
Chemistry 121, Summer 2013, LA Tech
13-68
Reactions of Benzene
The most characteristic reaction of aromatic
compounds is substitution at a ring carbon
Halogen ation :
H + Cl2
FeCl3
Cl + HCl
Ch lorobenzen e
N itration :
H + HNO3
H2 SO4
NO2 + H2 O
N itroben zene
Chemistry 121, Summer 2013, LA Tech
13-69
Chemistry 121, Summer 2013, LA Tech
13-70
Chemistry 121, Summer 2013, LA Tech
13-71
Chemistry 121, Summer 2013, LA Tech
13-72
Benzylic Oxidation
Benzene is unaffected by strong oxidizing agents
such as H2CrO4 and KMnO4
• halogen and nitro substituents are unaffected by these
reagents
• an alkyl group with at least one hydrogen on the
benzylic carbon is oxidized to a carboxyl group
CH3
O2 N
H2 CrO4
Cl
2-Chloro-4-n itrotoluene
Chemistry 121, Summer 2013, LA Tech
COOH
O2 N
Cl
2-Chloro-4-nitrob enzoic acid
13-73
Benzylic Oxidation
• if there is more than one alkyl group, each is oxidized
to a -COOH group
H3 C
CH 3
1,4-D imeth ylb enzene
(p-xylene)
H2 CrO4
O
HOC
O
COH
1,4-Benzened icarboxylic acid
(terep hthalic acid )
• terephthalic acid is one of the two monomers required
for the synthesis of poly(ethylene terephthalate), a
polymer that can be fabricated into Dacron polyester
fibers and into Mylar films
Chemistry 121, Summer 2013, LA Tech
13-74
Reactions of Benzene
Su lfonation:
H + H2 SO4
SO3 H +
H2 O
Benzen esulfonic acid
Alkylation:
H + RX
AlCl3
R + HX
An alk ylb enzene
Acylation:
H
O
+ R-C-X
An acyl
h alide
Chemistry 121, Summer 2013, LA Tech
AlCl3
O
CR + HX
An acylb enzene
13-75
Nitration
The electrophile is NO2+, generated in this way
H O NO2 + H O SO3 H
N itric acid
H
+
H O NO2
Chemistry 121, Summer 2013, LA Tech
H
H O
H
+
H O NO2 + HSO4
Conjugate acid
of n itric acid
+
+
NO2
The n itronium
ion
13-76
Friedel-Crafts Alkylation
Friedel-Crafts alkylation forms a new C-C bond
between an aromatic ring and an alkyl group
+
Benzene
Cl
AlCl3
2-Ch loropropan e
(Is op ropyl chloride)
Chemistry 121, Summer 2013, LA Tech
+ HCl
Isoprop ylb enzene
(Cumen e)
13-77
Friedel-Crafts Acylations
Treating an aromatic ring with an acid chloride in
the presence of AlCl3
• acid (acyl) chloride: a derivative of a carboxylic acid in
which the -OH is replaced by a chlorine
O
O
+
Benzene
CH3 CCl
Acetyl ch loride
(an acyl halid e)
Chemistry 121, Summer 2013, LA Tech
AlCl3
CCH3
+ HCl
Acetop henone
(a k eton e)
13-78