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CHEMISTRY
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1 BASIC CONCEPTS
HYDROCARBONS


Contain carbon and hydrogen only

SATURATED HYDROCARBONS
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Alkanes
Cycloalkanes

FUNCTIONAL GROUP


Molecules with the same functional group react in a similar way

SHAPE OF ALKANES
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Tetrahedral
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COOH

ESTER GROUP STRUCTURAL FORMULA
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COOR

ALDEHYDE GROUP STRUCTURAL FORMULA
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CHO

E/Z ISOMERISM
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Occurs because of the restricted rotation of the C=C bond

CRITERIA TO HAVE E/Z ISOMERISM
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A carbon-carbon double bond must be present
Each carbon in the double bond must be attached to two different groups
E-isomer has groups on opposite sides
Z-isomer has groups on same side

CIS-TRANS ISOMERISM
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Two of the substituent groups are the same attached to each carbon
Cis isomer has groups on the same side
Trans isomer has groups on opposite sides

BOND FISSION


Covalent bonds are broken

HOMOLYTIC FISSION
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Each bonded atom takes one of the shared pair of electrons
Forms two radicals

HETEROLYTIC FISSION
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One of the bonded atoms takes both of the shared pair of electrons
A cation and an anion are formed

NUCLEOPHILE
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Often negative ions with a lone pair of electrons
Attacks electron-deficient atoms
E
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:Br-, :OH-, H2O:, :NH3

ELECTROPHILE
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Often positive ions
Attacks electron-rich atoms
E
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Br2, HBr, NO2+

ADDITION REACTION
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2 reactants  1 product
Unsaturated  saturated

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1
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Octane is present in petrol

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Heavier rain
Violent storms
Rise in sea levels
Flooding

FUELS OF THE FUTURE
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Biofuel – fuel derived from plants or animal waste
Ethanol – fermenting sugar (carbohydrates)
Biodiesel – fuel derived from plants (rapeseed)

SUBSTITUTION REACTIONS OF ALKANES
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Radical substitution
 Homolytic fission to form radicals
 A hydrogen atom is substituted by a halogen atom

HALOGENATION OF ALKANES
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Alkanes react with halogens
Ultraviolet radiation (provides energy for bond fission)
Temperature of about 300⁰C
Forms halogenoalkanes

MECHANISM
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Initiation
Propagation (first and second)
Termination

MECHANISM FOR CHLORINATION (EXAMPLE)
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

Initiation
 Cl-Cl  Cl• + Cl•
Propagation
 CH4 + Cl•  •CH3 + HCl
 •CH3 + Cl2  CH3Cl + Cl•
Termination
 Cl• + Cl•  Cl2
 •CH3 + •CH3  C2H6
 •CH3 + •Cl  CH3Cl

LIMITATIONS OF RADICAL SUBSTITUTION
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Radical substitution forms a mixture of products
Other organic products can form (apart from products in propagation)
Halogenoalkane in propagation step may react with further Cl•
E
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CH2Cl2, CHCl3, CCl4

2
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3 ALKENES
UNSATURATED HYDROCARBONS


Alkenes

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Gases at room temperature

ADDITION OF HYDROGEN HALIDES
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Hydrogen halides are bubbled into liquid alkanes
E
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ethene + HBr  bromoethane

ADDITION OF STEAM (HYDRATION)
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Method of preparing alcohols
Steam + gaseous alkene
High temperature and pressure
In the presence of a phosphoric acid catalyst (H3PO4)
E
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ethene + H2O (g)  ethanol

ADDITION TO UNSYMMETRICAL ALKENES
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Results in two isometric products
E
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propene + HBr  2-bromopropane + 1-bromopropane

ELECTROPHILIC ADDITION REACTIONS
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Electrophiles are attracted to regions of high electron density (π-electrons)

ADDITION OF HYDROGEN BROMIDE
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Hydrogen bromide is a polar molecule
 Bromine is more electronegative
 Causes a dipole
 Electrophile
Electron pair in alkene (π-bond) is attracted to slightly positive hydrogen atom
Double bond breaks
Bond forms between a carbon and hydrogen atom
H-Br breaks by heterolytic fission
 Electron pair goes to Br
Br- and a carbocation are formed
Carbocation reacts with BrBromoethane formed

ADDITION OF BROMINE
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Test for unsaturation
Bromine is a non-polar molecule
Electrons in pi-bond and in Br-Br bond repel
Induces a dipole in Br2
Electron pair attracted to slightly positive Br atom
Br-Br breaks by heterolytic fission
Br- and a carbocation are formed
Carbocation reacts with Br1,2-dibromoethane formed

DRAWING THE MECHANISM OF ELECTROPHILIC ADDITION


Step 1

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Reclamation

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)
Non-hazardous processes
Degrade naturally

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