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Organic ChemistryOrganic Chemistry
LaboratoriumLaboratorium KimiaKimia OrganikOrganik JurusanJurusan KimiaKimia
FakultasFakultas MatematikanMatematikan dandan IlmuIlmu PengetahuanPengetahuan AlamAlam
UniversitasUniversitas PadjadjaranPadjadjaran
20092009
Dr.Dr. DikdikDikdik KurniaKurnia,, M.ScM.Sc
Alkenes, Alkynes, and Aromatic CompoundsAlkenes, Alkynes, and Aromatic Compounds
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Organic ChemistryOrganic Chemistry
Laboratorium Kimia Organik Jurusan Kimia
Fakultas Matematikan dan Ilmu Pengetahuan Alam
Universitas Padjadjaran
2009
Code of Lecture : D10B. 03E0318
The Unit of Semester credits (SKS) : 2 (2-0)
Semester : Fm/1
Day/Time : Thursday, 13.00 14.40 am
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Alkenes, Alkynes, and Aromatic Compounds
1. What are alkenes, alkyunes, and aromatic compounds?Be able to recognize the structure of members of these three families ofunsaturated organic compounds and give examples of each.
2. How are alkenes, alkyunes, and aromatic compounds named?Be able to name an alkene, alkyune, or simple aromatic compound fromits structure or write the structure, given name.
3. What are cis-trans isomers?Be able to identity cis-trans isomers and predict their occurrence.
4. What are the general properties of alkyunes, and aromatic compounds?Be able to describe and compare such properties as polarity, watersolubility, flammability, bonding, and chemical reactivity.
5. What are the common chemical reactions of alkyunes, and aromatic
compounds?Be able to predict the products of reactions ofalkyunes, and aromaticcompounds.
6. How do organic reactions take place?Be able to show how addition reaction occur and describe the differencebetween additon and substitution reactions.
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Alkenes, Alkynes, and Aromatic Compounds
Compounds in three families described in this chapter all contain carbon-
carbon multiple bonds;
a. Alkenes (ethlene), contain a carbon-carbon double bondb. Alkyunes (acetylene), contain a carbon-carbon triple bond
c. Aromatic compounds (benzene), contain a six-membered ring of carbon
atoms with three double bonds or other rings with similar arrangment of
alternating double bonds.
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Saturated and Unsaturated Hydrocarbons
Alkenes and Alkyunes contain carbon-carbon multiple bonds to which more
hydrogen atoms can be added and are therefore knows as unsaturated
hydrocarbons.
Alkenes are hydrocarbons that contain carbon-carbon doube bonds
Alkyunes are hydrocarbons that contain carbon-carbon triple bonds
CH3CH2CH3
CH3CH=CH3 CH3CH|CH3
The alkanes are often referred to as saturated hydrocarbons because each
carbon atom is fully saturated by bonds to the maximum number of
hydrogen atoms: No more hydrogen atoms can be added.
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Alkenes
Simple Alkenes are made in huge quantities by thermal cracking of natural gasand petroleum and are the basic building block of the vast petrochemical
industri, which produces organic chemicals from petroleum.
CH3(CH2)nCH3 H2 + CH4 + CH2=CH2 + CH2=CH2 + CH3CH2CH=CH2
750-900rC
F-Caroten (a polyalkene)
cis-polyisoprene (Natural rubber)
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Naming Alkenes and Alkynes
1. Name the parent compound
Find the longest chain containing the double or triple bond and name the
parent compound by adding the suffix ene or yne to the root for main chain.
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Naming Alkanes and Alkyunes
2. Number the carbon atoms in the main chain.
Beginning and the end nearer the multiple bond, number each carbon
atom in the chain.
If the multiple bond is an equal distance from the both ends, as in the
middle structure, begin numbering at the end nearer the first branchpoint.
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Naming Alkanes and Alkyunes
For the cyclic alkenes, the-ane ending of the cycloalkane is replaced by ene.
No numbers are needed for an unsubstituted cycloalkene.
In substituted cycloalkenes, the double-bond carbon atoms are numbered 1
and 2 so that the first substituent has the lower number:
2. Number the carbon atoms in the main chain.
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Naming Alkanes and Alkyunes
3. Write out the full name.
Identify and number branching substituents in the same way as for alkaes:
Assign number to the branching substituents on the chain and list them
alphabetically.
Use commas to separates numbers and use hyphens to separate words from
numbers.
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The Structure of Alkenes: cis-trans Isomerism
Alkenes and Alkyunes differ from alkanes in shapes because of their differet kinds of
bonds
Two carbons and four attached atoms that make up the double-bond functional
group always lie in planar.
Unlike in alkannes where free rotation around the C-C single bond occurs, there is no
free rotation around double bonds a new kind of isomerism is possible for
alkenes
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The Structure of Alkenes: cis-trans Isomerism
1-butene and 2-butene are isomers because their double bonds occur at different
positions along the chain.
Because of the rotation cant occur around carbon-
carbon double bonds, there are two different 2-
butenes.
1. The two methyl groups are close togetheron thesame side of the double bond.
2. The two methyl groups are far apart on opposite
sides of the double bond.
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The Structure of Alkenes: cis-trans Isomerism
Isomers, cis-trans: Alkenes that have the same formula and connections
between atoms but differ in having pairs of groups on opposite sides of the
double bonds.
cis- isomer: Isomer with a specific pairs of atoms or groups on the same side of
thedouble bond.
trans- isomer: Isomer with a specific pairs of atoms or groups on opposite side
of thedouble bond.
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The Structure of Alkenes: cis-trans Isomerism
cis-trans isomers occurs in an alkene whenever each double bond carbon is
bonded to two different substituents groups.If either double-bond carbond is attached to two identical cis-trans
isomerism is not possible.
These compounds are
identical, because the left-
hand carbon of the double
bond has two Hs attached,
cis-trans isomerism is
impossible
These compounds are notidentical, neither carbon of
the double bond has two
identical groups attached to
it
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Properties of Alkenes
Nonpolar: insoluble in water; soluble in nonpolar organic
solvent; less dense than water.
Alkaline-like in melting points, boiling points, and other
physical properties.
Flammable; gaseous alkenes not toxic. Display cis-trans isomerism when each double-bond C atom
has different substituents.
Chemically reactive at double bond, which undergous
addition reactions.
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Properties of Alkenes
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Chemical Reactions of Alkenes and Alkyunes
Most of the reaction carbob-carbon multiple bonds can be grouped under the
category ofaddition reactions, addition of a reactant of the general form X-Yto the multiple bond of an unsaturated compound to yield a saturated poduct.
Alkenes and alkynes react similarity in many ways, but well look at alkenes
because theyre more common and more important
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Chemical Reactions of Alkenes and AlkyunesAddition of Cl2 and Br2 to Alkenes (Halogenation)
Halogenation: The reaction of an alkene (or alkyne) with halogen (Cl2 or Br2) to
yiels a 1,2-dihaloalkane product.
Halogenation: The reaction of an alkene (or alkyne) with halogen (Cl2 or Br2) to
yiels a 1,2-dihaloalkane product.
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Chemical Reactions of Alkenes and AlkyunesAddition of HBr and HCl to Alkenes
An alkyl bromide
An alkyl chloride
Hydrohalogenation: The reaction of an alkene with HCl or HBr to yiels an alkyl
haide product.
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Chemical Reactions of Alkenes and AlkyunesAddition of HBr and HCl to Alkenes
Only one of the two possible addition products is obtained.
This is what usually happens when HBr and HCl add to alkenes with
unsymmetrically substituted double bonds, that is, double bonds in which
one carbon is bonded to more hydrogens than other
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Chemical Reactions of Alkenes and AlkyunesAddition of HBr and HCl to Alkenes
Markovnikovs rule: In the addition of HX to and alkene, the H becomesattached to the carbon that already has the most Hs,
and the X becomes attached to the carbon that has
fewer Hs.
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Chemical Reactions of Alkenes and AlkyunesAddition of H2O to Alkenes (Hydration)
Hydration, alkene: The reaction of an alkene with water (H2O) to yiels an alcohol.
This reaction occurs on treatment of the alkene with water in the presence of
astrong acid catalyst such as H2SO4.
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Chemical Reactions of Alkenes and AlkyunesAddition of H2O to Alkenes (Hydration)
Markovnikovs rule: In the addition of HX to and alkene, the H becomesattached to the carbon that already has the most Hs,
and the X becomes attached to the carbon that has
fewer Hs.
As with the addition of HBr and HCl, Markovnikovs rule can be used to predict
the product when water add to an unsymmetrically substituted alkene.
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How An Alkene Addition Reaction Occurs
Figure 13.2 A reaction mechanism of how the addition of HBr to an alkene occurs.
The reaction takes place in two steps and involves a carbocation intermediate.
Step 1Two electrons from the C-C double bonds are
used to form a new single bond between the
incoming hydrogen ion and one of the carbons.
The other carbon now has only six electrons in its
outer shell and has a positive charge
Step 2The positively charged carbocation then reacts
with the negatively bromide ion, using an
electron pair from bromide to form a single bondbetween carbon and bromine.
The second carbon thus regains an outer-shell
octet
Carbocation:A polyatomic ion with a
positively charged carbon
atom.
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Alkene Polymers
Polymer:
A very large molecule composed of identical repeating units and formed by the
combination of small molecules.
Vinil Monomer:
A compound with the structure CH2=CHZ that undergoes polymerization to give
a polymer with the repeating unit CH2CHZ
Monomer:
A small molecule combined to form a polymer
Polimerization:
A reaction in which monomers combine to form a polymer.
Chain-growth polymer:
A polymer formed by the addition of monomer molecules one by one to the end
of a growing chain.
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Alkene Polymers
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Alkynes
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Aromatic Compounds and The Structure of Benzene
Aromatic compound:A compound that contains a six-membered ring of carbon atoms with three
double bonds or a similarly stable ring.
Resonance:
The exixtance of a molecul in a single structure intermediate among two ormore correct possible double-bond-containing structure that can be drawn.
Benzene, The simplest aromatic compound, is a flat, symmetrical molecule with
the molecular formula C6H6 (cyclohexatriene)
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Aromatic Compounds and The Structure of Benzene
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Naming Aromatic Compounds
Ortho: Indicates 1,2 substituents on a benzene ring
Ortho: Indicates 1,3 substituents on a benzene ring
Ortho: Indicates 1,4 substituents on a benzene ring
No number is needed for monosubstituted benzene because all the ring
positions are equivalent.
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Naming Aromatic Compounds
Number must be included in the name when a benzene ring three or moresubstituents.
In the same manner as for alkane, the numbers are chosen so that substituents
have the lowest possible numbers and the substituents are named in
alphabetical order
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Naming Aromatic Compounds
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Naming Aromatic Compounds
Phenyl group: The name of the C6H5- unit when a benzene ring is considered a
substituent group.
Aryl group: The general name for any substituent derived from an aromatic
compound
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Chemical Reactions of Aromatic CompoundsAromatic Substitution Reactions
Substitution reaction Aromatic:
Substitution of an atom or group for one of the hydrogens on an aromatic ring.
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Chemical Reactions of Aromatic CompoundsAromatic Substitution Reactions
Nitration
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Chemical Reactions of Aromatic CompoundsAromatic Substitution Reactions
Halogenation
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Chemical Reactions of Aromatic CompoundsAromatic Substitution Reactions
Sulfonation
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Polycyclic Aromatic Compounds and Cancer