UNSATURATED
HIDROCARBONS
Unsaturated hidrocarbons contains
carbon-carbon double bonds.
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Alkene = olefin
Alkyne = acetylene
Aromatic compound = benzene ring
ALKENE
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Alkena disebut juga olefin
Unsaturated hidrocarbon
Double bond
Pembentuk minyak
Rumus: CnH2n
Sifat
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BM alkena < BM alkana
Titik didih alkena < alkana
Berat jenis alkena < air
Tidak larut dalam air & larut dalam
pelarut organik
Alkena lebih reaktif daripada alkana
Produksi alkena menghasilkan
alkana & alkohol
Nomenclature
(1)
1.
2.
Select the longest carbon-carbon chain
that cantains the double bond.
Name the parent compound as you
would an alkene but change the –ane
ending to –ene; for example, propane is
change to propene.
CH3 CH2 CH3
CH3CH=CH2
Propane
Propene
Nomenclature
(2)
3. Number the carbon chain of the parent
compound starting with the end nearer
to the double bond. Use the smaller of
the two numbers on the double-bonded
carbon atoms to indicate the position of
the double bond. Place this number in
front of the alkene name; for example,
2-butene means that the carbon-carbon
double bond is between carbon numbers
2 and 3.
Nomenclature
(3)
4. Side chains and other groups are
treated as in naming alkanes, by
numbering and assigning them to
the carbon atom to which they are
bonded.
College Chemistry_ch.22.2_p.551
Practice 1 :
Write structural formulas of :
1. 2-pentene
2. 7-methyl-2-octene
3. 3-hexene
4. 4-ethyl-2-heptene
5. 3,4-dimethyl-2-pentene
Geometric Isomerism in Alkenes
(1)
Geometric isomer
= isomer that differ from each other
only in the geometry of the
molecules and not in the order of
their atoms.
Geometric Isomerism in Alkenes
(2)
Geometric isomers are also called cis-trans isomers.
If the two chlorine atoms are locked on opposite sides of
the double bond, it is known as the trans isomer.
(trans : from latin meaning "across" - as in transatlantic).
If the two chlorine atoms are locked on the same side of
the double bond, it is known as the cis isomer.
(cis : from latin meaning "on this side")
Geometric Isomerism in Alkenes
(3)
Practise 2
Draw structural formulas and names
for all the isomers of pentene, C5H10.
Identify all geometric isomers.
Identify which one that have cis-trans
isomers, and draw the cis-trans
isomers.
Cycloalkenes
A cycloalkene or cycloolefin is a type of
alkene hydrocarbon which contains a
closed ring of carbon atoms, but has no
aromatic character.
cyclopropene cyclobutene
cyclopentene
cycloheptene
Preparation of Alkenes
Cracking/Pyrolisis
Adalah pemanasan hidrokarbon jenuh pada
suhu yang sangat tinggi dan dengan
bantuan katalis silika-alumina
Contoh:

C16H34
C8H18 + C8H16
alkane
alkane
alkene
Dehydration of Alcohols
Alkohol dipanaskan pada asam sulfat
terkonsentrasi
Reaksi:
Alkohol con.H2SO4
alkena + H2O

Contoh:
C – C – C – C +H2SO4
OH
 C – C = C – C +H2O
 C – C – C = C +H2O

Alkenes Physical Properties
The first three alkenes are gases, the intermediate alkenes are liquids and
higher members of the olefin series are wax like solids at room temperature.
The alkenes are insoluble in water, but are soluble in organic solvents. The
liquids and solids have a density less than water.
Compound
Formula
MP
oC
BP
oC
Density
(g/ml)
Ethylene
C2H4
C3H6
C4H8
-170
-102
0.6128
-185
-47
0.6142
-130
-6.5
0.6356
Propene
Butene
Chemical Properties of Alkenes
(1)
Combustion of Alkenes
The alkenes are highly flammable and burn
readily in air, forming carbon dioxide and water.
C2H4 + 3 O2  2 CO2 + 2 H2O
Chemical Properties of Alkenes
(2)
Addition:
 Addition of Hydrogen (hidrogenation)
 Addition of Halogen (halogenation)
 Addition of Hydrogen Halide
 Addition of Water
Chemical Properties of Alkenes
(3)
Addition Reactions across the Double
Bond (oxidation)
3 H2C=CH2 + 2 KMnO4 + 4 H2O
 2MnO2 + 2KOH + CH2OHCH2OH
Ethylene Glycol
During the oxidation of alkenes, the purple
colour of the permanganate solution
disappears and the reaction constitutes a test,
known as Baeyer's Test, to detect unsaturation
in any compound.
Chemical Properties of Alkenes
(4)
Reaction with Sulphuric Acid
Similarly, fuming sulphuric acid absorbs ethylene at
room temperature to form ethyl hydrogen sulphate, with
much evolution of heat.
C2H4 + H2SO4  C2H5.HSO4
If this is treated with water and warmed, ethanol is
formed.
heat
C2H5.HSO4 + H2O  C2H5OH + H2SO4
Chemical Properties of Alkenes
(5)
Polymerisation Reactions due to the Double Bond
When ethylene is heated under great pressure in the presence of a
catalyst a large number of the molecules combine to form
polythene, (C2H4)n, (i.e. Polyethylene). This particular kind of
reaction is called an addition polymerisation and the mechanism
by which it takes place is a reaction is a free radical chain reaction.
The overall reaction is
n(C2H4)  (C2H4)n
Ethene Polythene
Alkynes/Acetylene
Sifat:
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Sifat hampir sama dengan alkena
Berupa gas tidak berwarna
Tidak larut dalam air & gas
pada tekanan & suhu normal
Sangat mudah terdekomposisi
Sebagai asetilen cair, bersifat
sangat sensitif dan dapat meledak.
Nomenclature
The procedure for naming alkynes is
the same as that for alkenes, but
the ending used is –yne to indicate
the presence of a triple bond.
The name of some common alkynes :
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Molecular
Formula
Structural
formula
Common
name
IUPAC
name
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C2H2
C3H4
C4H6
C4H6
H-C≡C-H
CH3-C≡C-H
CH3CH2-C≡C-H
CH3-C≡C-CH3
Acetylene
Ethyne
Methylacetylene
Propyne
Ethylacetylene
1-Butyne
Dimethylacetylene2-Butyne
Prepraration
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From calcium carbide and water
CaC2 + 2 H2O  HC≡CH + Ca(OH)2
From cracking mathane
2 CH4  HC≡CH + 3 H2
Chemical Properties
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Hidrogenation
Halogenation
Hidrogen halida
Aromatic Hydrocarbon
Structure
Aromatic compounds
 benzene
 C6H6
Naming :
Monosubstitued Benzenes
Monosubstitued benzenes are named by
adding the name of the substituent
group as a prefix to the word benzene.
Examples :
Nitrobenzene
Ethylbenzene
Chlorobenzene
Bromobenzene
Certain monosubstitued benzenes have
special names.
Methylbenzene = Toluene
Hydroxybenzene = Phenol
Vinylbenzene =Styrene
Benzene carboxylic acid = Benzenic acid
Benzene carboxaldehyd = Benzaldehyde
Aminobenzene =Aniline
Toluene
Phenol
Styrene
Benzoic acid
Benzaldehyde
Aniline
C6H6– group is known as phenyl/venil
The name phenyl is used to name compounds that
cannot easily be named as benzene derivatives.
Example :
Naming :
Disubstitued Benzenes
Names  monosubstitued benzene
Except dimethylbenzene have special
name xylene.
Ortho, meta, and para substitution
Ketentuan
Ortho / para :
(dari yang paling kuat)
 NH2
 OR
 OH
 OCOR
R
X
Meta :
(dari yang paling kuat)
 NO2
 CN
 SO3H
 CHO
 COR
 COOH
 COOR
Naming :
Polysubstitued Benzenes
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When there are more than two
substituents on a benzene ring, the
carbon atoms in the ring are
numbered starting at one of the
substituted groups.
Polycyclic Aromatic Compounds
Chemical Properties
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Halogenation (chlorination/bromination)
Nitration
Alkylation (Friedel-Crafts reaction)
Oxidation of side chain