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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-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:

C

₁₆

H

₃₄ ^

C

₈

H

₁₈

+ C

₈

H

₁₆

alkane alkane

^alkene

Dehydration of Alcohols

Alkohol dipanaskan pada asam sulfat terkonsentrasi

Reaksi:

Alkohol

^con.H2SO4

alkena + H

₂

O 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 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 IUPAC

Formula formula name name

_________________________________________________

C₂H₂ H-C≡C-H Acetylene Ethyne

C₃H₄ CH₃-C≡C-H Methylacetylene Propyne C4H6 CH3CH2-C≡C-H Ethylacetylene 1-Butyne C₄H₆ CH₃-C≡C-CH₃ Dimethylacetylene2-Butyne

Prepraration

 From calcium carbide and water

CaC2 + 2 H2O  HC≡CH + Ca(OH)2

 From cracking mathane 2 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

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 : 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