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