UNSATURATED HIDROCARBONS
Unsaturated hidrocarbons contains carbon-carbon double bonds.
Alkene = olefin Alkyne = acetylene Aromatic compound = benzene ring
ALKENE
Alkena disebut juga olefin Unsaturated hidrocarbon Double bond Pembentuk minyak Rumus: CnH2n
Sifat
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. Select the longest carbon-carbon chain that cantains the double bond.
2. 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-pentene2. 7-methyl-2-octene3. 3-hexene4. 4-ethyl-2-heptene5. 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
OHC – C = C – C +H2OC – 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 BP Density oC oC (g/ml)
Ethylene C2H4 -170 -102 0.6128
Propene C3H6 -185 -47 0.6142
Butene C4H8 -130 -6.5 0.6356
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:
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 :_________________________________________________
Molecular Structural Common IUPACFormula formula name name_________________________________________________
C2H2 H-C≡C-H Acetylene EthyneC3H4 CH3-C≡C-H Methylacetylene PropyneC4H6 CH3CH2-C≡C-H Ethylacetylene 1-ButyneC4H6 CH3-C≡C-CH3 Dimethylacetylene2-Butyne
Prepraration
From calcium carbide and waterCaC2 + 2 H2O HC≡CH + Ca(OH)2
From cracking mathane2 CH4 HC≡CH + 3 H2
Chemical Properties
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 benzeneExcept dimethylbenzene have special
name xylene.
Ortho, meta, and para substitution
KetentuanOrtho / para : Meta :(dari yang paling kuat) (dari yang paling kuat) NH2 NO2
OR CN OH SO3H
OCOR CHO R COR X COOH
COOR
Naming : Polysubstitued Benzenes
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
Halogenation (chlorination/bromination) Nitration Alkylation (Friedel-Crafts reaction) Oxidation of side chain