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CHEMISTRY
I An introduction to organic chemistry
Petroleum & Natural gas
 Fractional distillation of Petroleum
Petroleum (________ oil) is a mixture of ________________.
Petroleum must be separated into ___________ before it can be useful.
The separation of petroleum into useful fractions is called ___________ the oil.
Each petroleum fraction is a mixture of hydrocarbons which boils over a certain
temperature range.
Principle behind fractional distillation of petroleum:
A hydrocarbon with a long carbon chain has a ________________________
than one with a shorter carbon chain. (physical property)
 The use of petroleum fractions
During fractional distillation, petroleum is separated into seven principal fractions.
Two main uses of petroleum fractions : as fuels and as chemical feedstocks.
 Fuels (e.g. coal, petroleum & natural gas)
In comparing fuels, four main important properties are considered: safety,
convenience, pollution & heat of combustion)
 Alternative fuels
Fossil fuels are non-renewable but fuels
obtained from plants and organic wastes are
renewable.
In future, hydrogen, alcohol, palm oil & biogas
may become important sources of fuel, esp when
fossil fuels get more expensive as supplies
become exhausted.
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The supply of coal, petroleum & natural gas is limited.
Other possible source of fuel are
- palm oil – e.g. Malaysia
- alcohol mixed with petrol is used to run vehicle engines. – Brazil (alcohol is
produced from sugar cane)
- Biogas – is the gas produced when organic matter (waste material from
plants or animals) is allowed to decay in the absence of air. Biogas contains
about 50% of methane.
- hydrogen
Homologous series
Is a family of organic compounds with similar chemical properties.
Compounds of the same homologous series contain the same functional group.
Four main homologous series:
Alkane, Alkene, alcohol & carboxylic acid.
Properties :
1. similar chemical properties
2. gradual change in their physical properties.
e.g. the melting point and boiling points rise gradually as the number of
carbon atoms in the molecule increases.
e.g. the viscosity of members of the same homologous series increases as
their size and mass increase.
Functional group
Any atom or group of atoms that gives the characteristic properties to a molecule
Naming organic compounds [Nomenclature]
Alkane
Full Structural
formula
Name
Methane
Alkene
Full Structural
formula
-
Name
-
Ethane
Ethene
Propane
Propene
Butane
Butene
Pentane
Pentene
Hexane
Hexene
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Alcohol
Full Structural
formula
CHEMISTRY
Name
Carboxylic acid
Full Structural
Name
formula
Methanol
Ethanoic acid
II Organic Chemistry - Alkanes
Physical properties
1. melting & boiling points increase as the relative molecular mass ___________.
Reason:
_______________________________________________________________
_______________________________________________________________
2. methane – butane are gases, pentane & hexane are liquids.
3. Viscosity increases as the relative molecular mass ___________ .
4. Flammability increases as the relative molecular mass ____________.
General formula of alkanes
Alkanes are hydrocarbons with the general formula CnH2n+2
Saturated hydrocarbon:
Because alkanes contain only ___________________ covalent bonds.
 Draw “dot and cross” diagram for methane and ethane.
 Draw full structural formulae for both methane and ethane.
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Isomerism
Compounds that have the same molecular formula but different structural formulae.
Example: C4H10
Draw all the possible structural formulae of the above alkane.
Straight-chain alkane
Branched-chain alkane
Chemical Properties
 Combustion
Alkanes burn readily in air when ignited by a spark or flame.
Combustion of alkanes in excess air/oxygen:
Equations:
1. Combustion of methane:
CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O(g)
2. Combustion of ethane:
Combustion of alkanes in insufficient supply of air/oxygen:
Combustion of methane:
 Substitution Reactions
Alkanes react with chlorine in the presence of UV light as a catalyst.
---to give a mixture of products.
Methane + chlorine → chloromethane + dichloromethane + trichloromethane +
tetrachloromethane + hydrogen chloride
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Mechanism: [Free radical substitution]
When alkanes react with halogen in the presence of UV light
e.g. CH4 react with Cl2
Step 1: Initiation step - Homolytic fission
UV
Cl
Cl
2 Cl ● [chlorine free radical]
Step 2: Propagation step
CH3
H + Cl●  HCl + CH3● [methyl free radical]
CH3● + Cl
Cl  CH3Cl + Cl●
…… chain reaction…….
where CH2Cl2 , CHCl3 [also known as chloroform] and CCl4 are also produced.
Step 3: Termination step – recombination of free radicals
Cl● + Cl●
 Cl2
CH3● + CH3●  C2H6
CH3● + Cl●
 CH3Cl
This process produces a mixture of chloromethane, dichloromethane, tricholomethane
& tetrachloromethane; they can then be separated by _______________.
Read more about Chloroform: http://www.chm.bris.ac.uk/motm/chloroform/chloroformv.htm
In the early 19th and early 20th centuries, chloroform was commonly used as an inhaled anaesthetic during
surgery. It was banned now due to its toxicity.
The fatal oral dose of chloroform is just 10ml due to respiratory or cardiac arrest. Prolonged exposure to
chloroform can cause liver damage.
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Question:
Octane, C8H18, is a hydrocarbon in petrol. Hexadecane, C16H34, is one of the
hydrocarbons in ship fuel.
(i)
Show by calculation that hexadecane contains a higher percentage of carbon
by mass than octane.
This is the equation for the complete combustion of octane.
2 C8H18 (l) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (g)
(ii)
Write an equation for the complete combustion of hexadecane.
(iii)
Use the equations to explain why hexadecane burns with a smokier
flame than octane.
(d) Name two fuels, suitable for cars, which do not come from crude oil.
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III Organic Chemistry - Alkenes
Alkenes
are compounds that contain one or more carbon-carbon double bond.
Unsaturated hydrocarbon
Refer to molecules which contain double bonds or triple bonds between carbon
atoms.
Physical properties
 Ethene, propene and butene are all _________ at room temperature.
 The boiling point of an alkene ________ as the number of carbon atoms in the
molecule increases.
General formula __________________
Electronic structure of ethene
Draw “dot & cross” diagram for ethene.
Isomerism
Draw all the possible full structural formulae of C4H8.
The branched-chain unsaturated hydrocarbon has __________ boiling point than
the straight-chain unsaturated hydrocarbon
Catalytic cracking of petroleum
Cracking:
The breaking down of a long-chain hydrocarbon into __________________.
over a solid catalyst.
e.g. alkanes → possible products are (smaller alkanes + alkenes + hydrogen)
Conditions: catalyst : aluminium oxide and silicon dioxide
Heat
1. C 18 H 38 → C8H18 + _________
2. C 18 H 38 → 6 C2H4 + _________
3. C 18 H 38 → C18H36 + _________
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Chemical Properties of alkenes
 Combustion reaction
C3H6 + O2 →
(complete combustion)
If it is incomplete combustion, some ____________ and ___________
are produced.
Note: Alkenes produce ______ soot than alkanes when they burn in air.
Because alkenes has __________ carbon content than alkanes.
 Addition reaction
Is a reaction in which an unsaturated organic compound combines with another
element or compound to form a single new compound.
 Hydrogenation (reaction between alkene & hydrogen)
e.g.
Conditions: catalyst: nickel
Temperature :2000C
Industrial importance:
used to change vegetable oil (liquid oil) into margarine(solid fat).
 Bromination (halogenation) ***chemical test for unsaturated
hydrocarbon.
* liquid bromine or aqueous bromine is reddish brown.
e.g.
Condition: at room temperature
Liquid bromine is _______________ when react with alkenes.
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 Hydration (reaction between alkenes and steam)
e.g.
Conditions: catalyst-phosphoric(V) acid
High temperature & pressure
 Addition polymerisation
Conditions: high temperature :2000C
High pressure :1000 atmospheric pressure
Suitable catalyst.
e.g.
Uses of poly(ethene)
-
used for making plastics, bags, toys, buckets. etc.
plastic film for wrapping fresh vegetables and meat.
**Compare saturated & unsaturated hydrocarbon.
Reagent: liquid or aqueous bromine
Condition: room temperature
Method:
Pass unknown hydrocarbon through liquid/aqueous bromine.
OR a few drops of the bromine solution is shaken with an unknown hydrocarbon.
Observation:
(1) the ________________ bromine turn colourless rapidly. This indicates that the
unknown is an unsaturated hydrocarbon.
(2) the ________________ bromine remain unchanged. This indicates that the
unknown is a saturated hydrocarbon or it is not an unsaturated hydrocarbon.
This is a chemical test used to detect the presence of a _________bond between two
carbon atoms.
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** Compare reaction mechanism
1. Free radical substitution
When alkanes react with halogen in the presence of UV light
e.g. CH4 react with Cl2
Step 1: Initiation step - Homolytic fission
UV
Cl
Cl
2 Cl ● [chlorine free radical]
Step 2: Propagation step
CH3
H + Cl●  HCl + CH3● [methyl free radical]
CH3● + Cl
Cl  CH3Cl + Cl●
…… chain reaction…….
where CH2Cl2 , CHCl3 [also known as chloroform] and CCl4 are also produced.
Step 3: Termination step – recombination of free radicals
Cl● + Cl●
 Cl2
CH3● + CH3●  C2H6
CH3● + Cl●
 CH3Cl
This process produces a mixture of chloromethane, dichloromethane, tricholomethane
& tetrachloromethane; they can then be separated by _______________.
Read more about Chloroform: http://www.chm.bris.ac.uk/motm/chloroform/chloroformv.htm
In the early 19th and early 20th centuries, chloroform was commonly used as an inhaled anaesthetic during
surgery. It was banned now due to its toxicity.
The fatal oral dose of chloroform is just 10ml due to respiratory or cardiac arrest. Prolonged exposure to
chloroform can cause liver damage.
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2. Electrophilic addition - Reaction involves alkenes
e.g. C2H4 react with Br2
Step 1:
Bromine molecule is polarized by the carbon carbon double bond in ethene.
Electrophile is produced.
H
H
H
C=C
H
Brδ+
H
Brδ-
H
H C–C H
+
Br
H
H
H–C–C-H
Br
Br
Br-
Step 2:
Brδ+ , an electrophile attacks carbon carbon double bond and produce a positively
charged carbon atom.
Step 3:
The highly unstable positively charged carbonium ion then react with Bromide ion by
accepting a pair of electrons to form C-Br bond.
*************************************************************************************************************
Write down the reaction mechanism for the reaction between ethene and hydrogen bromide.
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IV Organic Chemistry – Alcohols
Nomenclature
Aliphatic alcohols have the general formula of CnH2n+1OH.
or ROH where R is an alkyl group, if OH is replaced by H, it is regarded as
alkanes, hence it is also known as alkanols.
The functional group is –OH, hydroxyl group.
Ethanol is the most important member in this homologous series and is often
referred to as ‘alcohol’
Name the following alcohols:
(a) CH3CH2CH2OH ___________________
(b) CH3OH __________________________
(c) CH3CH(OH)CH3 __________________________
Draw the Full structural formula of the following alcohols:
(a) butanol
(b) propan-2-ol
(c) 2-methylpropan-2-ol
Physical Properties
** what is the pH of alcohol ? Is alcohol acidic or alkaline ?
Volatility/Boiling point
 Aliphatic alcohols with less than 12 carbon atoms are liquids at room
temperature.
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 Compare the boiling point of ethanol [780C] and propane [-420C].
Both have comparable relative molecular mass of 46, but the force of attraction
_______________________________________________________________
between propane molecules is weak van der Waals’ force [or instantaneous
_______________________________________________________________
dipole induced dipole attraction]. Whereas there is a stronger hydrogen
_______________________________________________________________
bonding between ethanol molecules due to the highly polar nature of the
_______________________________________________________________
–Oδ- – Hδ+ group. Hence larger amount of energy is needed to overcome the
_______________________________________________________________
Stronger hydrogen bond between ethanol molecules than the weaker Van
_______________________________________________________________
der Waals force between propane molecules.
_______________________________________________________________
Solubility
In water:
 Lower alcohols are soluble in water because they form hydrogen bonds with
water molecules
Draw a diagram to show the hydrogen bonding between ethanol and water.
 Solubility of alcohols in water decreases with increasing carbon number. Alcohol
with longer carbon chain is immisicible with water because it is less polar.
In organic solvents:
 The non-polar hydrocarbon part of the alcohol molecule enables alcohols to
dissolve organic solvents like hexane.
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Industrial sources of ethanol
 Hydration(or hydrolysis) of alkenes [ ____________ reaction]
H3PO4
C=C
+ H2O
300oC , 70 atm
 Fermentation
(a) starch or sugar solution + yeast
** yeast is a living plant, containing the enzyme which catalyses the
reaction.
yeast
C6H12O6
2 C2H5OH + 2CO2
30-35oC
Under anaerobic conditions
(b) Note: air must not allowed to come into contact with the solution, or
souring of the wine might take place (due to bacterial _____________
of ethanol to ethanoic acid).
(c) ethanol produced from fermentation contain only about 12% ethanol.
Why does the fermentation stop once this % is reached?
___________________________________________________________
(d) What method is needed to increase the % of ethanol using fermentation ?
____________________________________________________________
Chemical reactions of alcohols
 Combustion reaction
C2H5OH(l) + 3 O2(g)  2 CO2 (g) + 3H2O (l)
Burns with a pale blue flame under good supply of oxygen.
Burns with a yellow flame and soot is formed with limited supply of oxygen
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 Oxidation reaction
Cr2O72- / H+
CH3CH2OH + 2 [O]
CH3COOH + H2O
reflux
Reagent: acidified potassium dichromate(VI) or
acidified potassium manganate(VII)
Condition: heat with reflux
Observation: ________ acidified KMnO4 turns _____________.
________ acidified K2Cr2O7 turns ______________.
 Dehydration reaction
excess concentrated sulfuric acid
CH3CH2OH
+ H2O
heat at 170oC
_________________
 Esterification reaction [reversible reaction!!]
O
CH3CH2O-H + CH3C
OH
[ethanol]
O
CH3C
[ethanoic acid]
+ H2O
OCH2CH3
[ethyl ethanoate]
Conditions: reflux in the presence of small amount of concentrated sulfuric acid.
Function of concentrated sulfuric acid: ___________________
This reaction involves breaking the C-O single bond of the carboxyl group and
the O-H bond in the alcohol. [proved by isotopic labeling]
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V Organic Chemistry – Carboxylic acids
Nomenclature
Aliphatic carboxylic acids have the general formula of CnH2n+1COOH.
or RCOOH where R is an alkyl group.
O
The functional group is C–OH, [CO2H] , carboxyl group.
Name the following carboxylic acids:
(a) CH3CH2COOH ___________________
(b) HCOOH __________________________
Draw the Full structural formula of the following carboxylic acids:
(a) butanoic acid
(b) ethanedioic acid
Physical Properties
 Carboxylic acid is a weak acid with pH of ~4
 Boiling point
Carboxylic acids have relatively high boiling points due to the presence of
____________ bond between molecules.
Draw a diagram to show the interaction between molecules:
 Solubility
1. Methanoic and ethanoic acids are completely miscible in water because they
form ____________ bond with water molecules.
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2. Solubility in water _____________as the carbon chain length increases and
the molecules become less polar.
Explain the following phenomenon:
1.
Mr
CH3CO2H
60
CH3CH2CH2OH
60
b.p. / oC
118
97
2. At temperature just above 118oC, gaseuous ethanoic acid has Mr of 120 instead
of 60.
Formation of carboxylic acids
Oxidation of alcohols
e.g.
Cr2O72- / H+
CH3CH2OH + 2 [O]
CH3COOH + H2O
reflux
Reagent: acidified potassium dichromate(VI) or
acidified potassium manganate(VII)
Condition: heat with reflux
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Chemical reactions of carboxylic acids
 Reaction with bases, carbonates and reactive metals
CH3COOH + NaOH  CH3COONa + H2O
[sodium ethanoate]
2 CH3COOH + Na2CO3  2 CH3COONa + H2O + CO2
2 CH3COOH + 2Na  2 CH3COONa + H2
 Formation of esters
Use the displayed formula to show the reaction between propanoic acid and
ethanol:
VI Esters
Characteristics
 Esters have lower boiling points than carboxylic acids as they cannot form
hydrogen bond.
 Esters are insoluble in water.
 Esters have strong fruity smell.
Nomenclature
HCOOCH3 methyl methanoate
CH3COOC2H5 ________________________
CH3CH2COOCH2CH2CH3 _____________________________
Ethyl ethanoate ________________________
Propyl butanoate _________________________
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VII Organic Chemistry – Macromolecules
Addition polymers
Condensation polymers
Uses of synthetic polymers
Plastic waste & pollution
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 THE END 
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