1 13-1 Chemistry 121, Winter 2011, LA Tech Introduction to Organic Chemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) E-mail: [email protected]Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours: MWF 8:00 am - 10:00 am; TT 9:00 – 10:00 am & 1:00-2:00 pm. December 17, 2010 Test 1 (Chapters 12-13) January 19, 2011 Test 2 (Chapters 14,15 & 16) February 7, 2011 Test 3(Chapters 17, 18 & 19) February 23, 2011 Test 4 (Chapters 20, 21 & 22) February 24, 2011 Comprehensive Make Up Exam: Chemistry 121(01) Winter 2010-11 13-2 Chemistry 121, Winter 2011, LA Tech Chapter 13: Unsaturated Hydrocarbons Sections 4.1-4.5 13-3 Chemistry 121, Winter 2011, LA Tech 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 13-4 Chemistry 121, Winter 2011, LA Tech IUPAC Nomenclature of Alkyne CAG 13.2
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13-1Chemistry 121, Winter 2011, LA Tech
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
saturated hydrocarbons (CnH2n+2). Two hydrogen are
considered as unit of unstauration
13-10Chemistry 121, Winter 2011, LA Tech
• 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
C C
H
H H
121.7°
Ethylene
H
C C
CH3
H H
124.7°
Propene
Structure of Alkenes
13-11Chemistry 121, Winter 2011, LA Tech
→ Fig. 13.1 In ethene, the atoms are in a flat rather than a tetrahedral arrangement.
Bonding in ethene (ethylene)
13-12Chemistry 121, Winter 2011, LA Tech
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
4
13-13Chemistry 121, Winter 2011, LA Tech
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
13-14Chemistry 121, Winter 2011, LA Tech
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 hydrogenas carbon
13-15Chemistry 121, Winter 2011, LA Tech
Alkenes: Naming and Structures
One simple class of compound is the alkene
which has only C, H and single bonds.
• ethene propene 2- butene
• C2H4 C3H6 C4H8
• CH2CH2 CH3CH2CH2 CH3CH2CHCH3
13-16Chemistry 121, Winter 2011, LA Tech
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
5
13-17Chemistry 121, Winter 2011, LA Tech
IUPAC Nomenclature of Alkynes
• 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
triple bond the lower number
• follow IUPAC rules for numbering and naming
substituents
3-Methyl-1-butyne 6,6-Dimethyl-3-heptyne
11
2 2
3
3 44 5
6 7
13-18Chemistry 121, Winter 2011, LA Tech
Example of IUPAC Nomenclature of Alkenes
Cycloalkanes
1-Hexene 4-Methyl-1-hexene
2-Ethyl-3-methyl-1-pentene
1 1
1
2 2 2
3 3
34 4 4
5 5
56 6
1 2
3
4
5
3-Methylcyclo-pentene
CH3
1,6-Dimethylcyclo-hexene
CH3
CH31
65
4
3
2
13-19Chemistry 121, Winter 2011, LA Tech
Nomenclature of Alkenes: Common Names
Some alkenes, particularly low-molecular-weight ones, are
known almost exclusively by their common names
CH2=CH2 CH3CH=CH2 CH3C=CH2
CH3
IUPAC:
IsobutylenePropyleneEthyleneCommon:
2-MethylpropenePropeneEthene
13-20Chemistry 121, Winter 2011, LA Tech
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”
6
13-21Chemistry 121, Winter 2011, LA Tech
Physical state summary for unbranched 1 alkynes at room temperature and pressure.
Physical State of Alkynes
13-22Chemistry 121, Winter 2011, LA Tech
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.
13-23Chemistry 121, Winter 2011, LA Tech
Fig. 13.2 A comparison of structural isomerism possibilities for four and five-carbon alkane and alkene systems.
Isomerism in Alkanes & Alkenes
13-24Chemistry 121, Winter 2011, LA Tech
← Fig. 13.3 Cis-trans isomers: Different representatives of the cisand trans isomers of 2-butene.
Cis-trans isomerism in 2-butene
7
13-25Chemistry 121, Winter 2011, LA Tech
Unsaturated Aromatic Hydrocarbons
CC 13.2
13-26Chemistry 121, Winter 2011, LA Tech
Geometrical Stereoisomerism
Because of restricted rotation about a C-C double bond,
groups on adjacent carbons are either cis or trans to
each other
cis-2-Butenemp -139°C, bp 4°C
t rans-2-Butenemp -106°C, bp 1°C
C
H3 C
C
H
CH3
C
HH
C
CH3
HH3 C
13-27Chemistry 121, Winter 2011, LA Tech
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
13-28Chemistry 121, Winter 2011, LA Tech
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
8
13-29Chemistry 121, Winter 2011, LA Tech
Summary of Physical State of Unsaturated
Hydrocarbons
13-30Chemistry 121, Winter 2011, LA Tech
Geometric isomers
There are two possible arrangements.
Example 2-butene
C=C
H
CH3
H3C
H
C=C
CH3
HH
H3C
cis Largest groups areon the same side.
transLargest groups areon opposite sides.
13-31Chemistry 121, Winter 2011, LA Tech
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
• cyclooctene is the smallest cycloalkene that can accommodate a
trans double bond
H
H
CH3
C H3
t rans-Cyclooctene cis-Cyclooctene13-32Chemistry 121, Winter 2011, LA Tech
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
C2 -C3 C4 -C5
Double bond
trans trans
trans cis
cis trans
cis cis
t rans,t rans-2,4-heptadiene
trans ,cis-2,4-heptadiene
2 2
4 4
9
13-33Chemistry 121, Winter 2011, LA Tech
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
Vitamin A aldehyde (retinal)
enzyme-catalyzed
oxidation
H
OVitamin A (retinol)
OH
13-34Chemistry 121, Winter 2011, LA Tech
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
2-Methyl-1,3-butadiene (Isoprene)
12
34head tail
13-35Chemistry 121, Winter 2011, LA Tech
Terpenes with isoprene units
13-36Chemistry 121, Winter 2011, LA Tech
Terpenes: Polymers of Isoprene
• myrcene, C10H16, a
component of bayberry
wax and oils of bay and
verbena
• menthol, from
peppermint
OH
10
13-37Chemistry 121, Winter 2011, LA Tech
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
13-38Chemistry 121, Winter 2011, LA Tech
Reactions of Unsaturated HydrocarbonsCAG 13.1
13-39Chemistry 121, Winter 2011, LA Tech
Reactions of alkenes
Combustion
C2H4 + 4 O2 2 CO2 + 2 H2O + heat
Alkynes also under go combustion reactions
similarly
13-40Chemistry 121, Winter 2011, LA Tech
Addition Reactions
The exposed electrons of double bonds make
alkenes more reactive than alkanes and
show addition reactions.
11
13-41Chemistry 121, Winter 2011, LA Tech
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.
Addition Reaction of Alkenes
13-42Chemistry 121, Winter 2011, LA Tech
→ 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.
Addition of Bromines
13-43Chemistry 121, Winter 2011, LA Tech
Vladimir Markovnikov synthesized rings containing four carbon atoms and seven carbon atoms.