Organic Chemistry
1. Organic chemistry is a branch of chemistry connected with compounds of hydrogen and carbon
(hydrocarbons).
2. Hydrocarbons: It is a class containing only hydrogen and carbon bonded together covalently. They
can form very long chains, and can form chains linked by one double bond or triple bond.
3. Homologous series: It is a family of compounds with same functional group and general formula
with similar physical and chemical properties.
4. Characteristics of homologous series:
(a) They have a general formula.
(b) They differ in molecular formula.
(c) A homologous series have similar chemical properties.
(d) Their physical properties are in a trend.
(e) Each homologous series have a functional of group.
(f) Each member in a homologous series differs in molecular formula from next by CH2.
Naming Organic Molecules
5. First part tells how many carbons the
molecule has:
6. The second part tells what type of molecule
it has:
7. Alkane – general formula CnH2n+2
8. Alkene – functional group: C=C bond, general formula: CnH2n
9. Alcohol – functional group: −OH, general formula: CnH2n+1OH
10. Carboxylic acid – functional group: −COOH, general formula: CnH2n+1COOH
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Homologous
Series
1 carbon
Molecular formula
Displayed formula
Structural formula
2 carbons
Molecular formula
Displayed formula
Structural formula
3 carbons
Molecular formula
Displayed formula
Structural formula
4 carbons
Molecular formula
Displayed formula
Structural formula
5 carbons
Molecular formula
Displayed formula
Structural formula
Alkane CnH2n+2
Alkene CnH2n
(C=C bond)
Methane (CH4)
CH4
Ethane (C2H6)
Alcohol CnH2n+1OH
(−OH)
Methanol (CH3OH)
Carboxylic acid
CnH2n+1COOH (−COOH)
Methanoic acid (HCOOH)
Ethene (C2H4)
CH3OH
Ethanol (C2H5OH)
HCOOH
Ethanoic acid (CH3COOH)
CH3CH3
Propane (C3H8)
CH2=CH2
Propene (C3H6)
CH3CH2OH
Propanol (C3H7OH)
CH3COOH
Propanoic acid (C2H5COOH)
CH3CH2CH3
Butane (C4H10)
CH2=CHCH3
Butene (C4H8)
CH3CH2CH2OH
Butanol (C4H9OH)
CH3CH2COOH
Butanoic acid (C3H7COOH)
CH3CH2CH2CH3
Pentane (C5H12)
CH2=CHCH2CH3
Pentene (C5H10)
CH3CH2CH2CH2OH
Pentanol (C5H10OH)
CH3CH2CH2COOH
Pentanoic acid (C4H9COOH)
CH3CH2CH2CH2CH3 CH2=CHCH2CH2CH3 CH3CH2CH2CH2CH2CH2OH
CH3CH2CH2CH2COOH
11. Isomers are compounds with the same molecular formula but different structural formula.
12. Structural isomers: have the same chemical formula, but different structures, they can be straight
or branched.
13. When naming an isomer, mention the position number of the alkyl radical.
14. Then, mention the position number of the functional group (eg C=C and −OH).
15. Isomers have different properties because they have different structures.
16. E.g, boiling point – Pentane has the highest boiling point because of its regular shape (regular
arrangement = strong forces of attraction) and this allows a bigger surface area for intermolecular
forces to work over and so requires more energy to overcome.
17. 2-methylbutane and 2,2-dimethylpropane have less regular shapes, weaker intermolecular forces
and therefore a lower boiling point.
2-methylbutane
2,2-dimethylpropane
But-1-ene
But-2-ene
2-methylprop-1-ene
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18. Isomers of Pentene (C5H10)
Pent-1-ene
Pent-2-ene
19. Isomers of propanol (C3H7OH)
20. Isomers of butanol (C4H9OH)
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Esters of carboxylic acids
21. Esterification – the esters formed when an alcohol reacts with a carboxylic acid.
22. For example, ethyl ethanoate is formed by the reaction between ethanol and ethanoic acid:
ethanoic acid + ethanol → ethyl ethanoate + water
CH3COOH(l) + C2H5OH(l) → CH3COOC2H5(l) + H2O(l)
23. Esters are named after the acid from which they are formed, ethanoate is the second part of this
name.
24. The alkyl group from the alcohol, ethyl, is the first part of this name.
25. Isomers of C4H8O2 esters.
Ethyl Ethanoate
Chemical Reactions of Alkanes
1. Complete combustion
(a) If air is present enough, then alkanes burn completely to produce carbon dioxide and water.
(b) alkane + oxygen → carbon dioxide + water
(c) CH4 + 2O2 → CO2 + 2H2O
2. Incomplete combustion
(a) If the air is not enough then alkanes burn incompletely and produce carbon monoxide or soot
(carbon) and water.
(b) Carbon monoxide (CO) is toxic because it interferes with the transport of oxygen around our
bodies by our red blood cells.
(c) alkane + oxygen → carbon monoxide + water
(d) 2CH4 + 3O2 → 2CO + 4H2O
3. Substitution reaction (Photochemical reaction)
(a) They will however react with chlorine and bromine in the presence of sunlight.
(b) A chlorine atom replaces a hydrogen atom. This can happen to all of the hydrogen atoms if
there is enough chlorine.
(c) CH4 + Cl2 → CH3Cl + HCl
(d) C2H6 + Br2 → C2H5Br + HBr
4. Cracking
(a) Long chain alkanes can be broken down into smaller more useful alkanes and alkenes.
(b) Cracking of ethane will give ethene and hydrogen.
Cracking Conditions:
i. 500°C
ii. Catalyst: Aluminium Oxide
or Silica
(c) Dodecane → Decane + Ethene
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Test for unsaturated compounds
1. Saturated hydrocarbons:
(a) only have single bonds
(b) do not react with aqueous bromine, so the mixture stays orange.
2. Unsaturated hydrocarbons:
(a) have double bonds
(b) react with aqueous bromine, turning the mixture from orange to colourless.
Chemical Reactions of Alkenes
1. Alkenes are similar to other hydrocarbons when burnt.
2. When alkenes burn in sufficient oxygen, they give carbon dioxide and water vapour.
ethene + oxygen → carbon dioxide + water
C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)
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Comparing the methods of ethanol production
Fermentation
The yeast undergoes anaerobic respiration, and
releases enzymes which catalyse the breakdown of
glucose to ethanol and carbon dioxide.
From ethene
The ethene reacts with steam (reversibly) in
the following conditions: 570°C, 60atm and a
catalyst (phosphoric acid).
Advantages:
• renewable source
• good use of waste organic material
Advantages:
• fast
• continuous process
• pure ethanol
• smaller containers
Disadvantages:
• oil is a non-renewable resource
• lots of energy to make steam and get the
right conditions
• a lot of ethene is un-reacted, (and then
recycled)
Disadvantages:
• Lots of material needed to produce just 1 litre of
ethanol so lots of big fermentation tanks needed.
• ethanol must be purified by fractional distillation
which is expensive
• Slow process
• Batch process
Uses of ethanol
1. Solvent: to dissolve the things than water cannot. It evaporates easily, so it is used a solvent in
glues, printing inks, perfumes and aftershave.
2. Fuel: added to or instead of petrol, because it burns cleanly with a clear flame, giving out a lot of
heat:
ethanol + oxygen → carbon dioxide + water
C2H5OH(l) + 3O2(g) → 2CO2(g)+ 3H2O(g)
Formation of ethanoic acid by oxidation of ethanol
1. By fermentation – the biological way
(a) When ethanol is left standing in air, bacteria bring about its oxidation to ethanoic acid. This
method is called acid fermentation.
(b) Acid fermentation is used to make vinegar (a dilute solution of ethanoic acid). The vinegar
starts as foods such as apples, rice, and honey, which are first fermented to give ethanol.
2. Using oxidising agents – the chemical way
(a) Ethanol is oxidised much faster by warming it with the powerful oxidising agent potassium
manganate(VII), in the presence of acid.
(b) The colour of the potassium manganate(VII) solution turns from purple to colourless.
ethanol + oxygen → ethanoic acid + water
from oxidising agent
C2H5OH + 2[O] → CH3COOH + H2O
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Reactions of ethanoic acid as an acid
1. Ethanoic acid is a weak acid which only partially dissociates into ions in water.
2. The solution does contain an excess of hydrogen ions (H+) over hydroxide ions (OH−), so the
solution is weakly acidic:
ethanoic acid ⇌ ethanoate ions + hydrogen ions
CH3COOH(aq) ⇌ CH3COO−(aq) + H+(aq)
3. Ethyl ethanoate is just one example of an ester.
Ethanoic acid + ethanol ⇌ ethyl ethanoate + water
(alcohol = -yl & carboxylic acid = -oate)
4. The ester family of compounds have strong and pleasant smells.
5. Many of these compounds occur naturally as the flavours in fruits and for the scents of flowers.
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6. We use them as food flavourings and in perfumes.
7. The ester group or linkage is also found in complex molecules such as natural fats and oils, and in
man-made polyester fibres.
(bromine water
changed from orange
to colourless)
Esterification
H SO catalyst
2
4
Ester
CH3COC2H5
Ethyl ethanoate
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Chapter 20: Petrochemicals and polymers
The fossil fuels
➢ The fossil fuels are petroleum (or crude oil), coal, and natural gas.
➢ They are called fossil fuels because they are the remains of plants and animals that lived millions of
years ago.
➢ Petroleum formed from the remains of dead organisms that fell to the ocean floor; and were buried
under thick sediment. High pressures slowly converted them to petroleum, over millions of years.
➢ Natural gas is mainly methane. It is often found with petroleum. It is formed in the same way. But
high temperatures and high pressures caused the compounds to break down to gas.
➢ Coal is the remains of lush vegetation that grew in ancient swamps. The dead vegetation was buried
under thick sediment. Pressure and heat slowly converted it to coal, over millions of years.
What is in petroleum?
➢ Petroleum is a smelly mixture of hundreds of different compounds.
➢ These fossil fuels all contain hydrocarbons.
➢ The formation of these fuels took place over many millions of years. These fuels are therefore a
non-renewable and finite resource.
Refining petroleum
➢ At oil refinery, petroleum can be separated by fractional distillation as each fraction has different
boiling point:
➢ Petroleum is heated and passed into a fractionating column or tower
➢ Small molecules rise to the top and the large ones stay at the bottom
➢ Different fractions are collected at different heights
➢ A fraction is a group of compounds with similar boiling points
b/p(℃)
25
40
110
180
220
250
300
350
Fraction
refinery gas
petrol (gasoline)
naphtha
kerosene
diesel oil
fuel oil
lubricating
bitumen
Uses
bottled gas – heating, cooking
fuel (petrol) in cars
making chemicals
jet fuel, lamps
fuel in diesel engines
fuel in ships, home heating
lubricants, waxes and polishes
making roads
Small molecules:
• low boiling point
• very volatile
• flows easily
• burn easily
• low viscosity
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Polymers
❖ Polymers are large organic molecules and are made up of many small repeating units known as
monomers joined together by polymerisation.
❖ 2 types of polymerisation:
➢ Addition polymerisation
➢ Condensation polymerisation
Addition polymerisation
❖ Only occurs in monomers that contain double carbon(C=C) bonds
❖ Polymers produced using alkene monomers
❖ Forms only a polymer molecule
❖ Poly(ethene) / Polythene: is a polymer produced from ethene by addition polymerisation
Double bond splits and polymer is formed
❖ Example of addition polymers
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Polymer (and trade name(s))
Properties
Examples of use
poly(ethene) (polyethylene,
polythene, PE)
tough, durable
plastic bags, bowls, bottles,
packaging
poly(propene) (polypropylene, PP)
tough, durable
crates and boxes, plastic
rope
poly(chloroethene) (polyvinyl
chloride, PVC)
strong, hard (not as flexible
as polythene)
insulation, pipes and
guttering
poly(tetrafluoroethene)
(polytetrafluoroethylene, Teflon,
PTFE)
non-stick surface, withstands
high temperatures
non-stick frying pans, nonstick taps and joints
poly(phenylethene) (polystyrene, PS) light, poor conductor of heat
insulation, packaging (foam)
❖ Deduce the relationship between monomer and addition polymer
From monomer to polymer
From polymer to monomer
•
draw the monomers with their double bonds
next to each other
•
•
remove the double bonds and draw single
bonds in the space between the monomers
identify the repeating unit - it will have two
carbon atoms with a single bond between
them; put a bracket round it
•
draw that unit as a separate molecule with a
double bond in it
Condensation Polymerization:
❖ When 2 different monomers are linked together with the removal of a smaller molecule, usually
water (forms one H2O molecule per linkage).
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❖ Nylon [polyamide] is made from a dicarboxylic acid monomer and an amine monomer (compound
with an NH2 functional group).
❖ Forms amide linkage.
❖ The fibres can be woven into fabric to make shirts, ties, sheets and so on, or turned into ropes, nets
or racket strings.
❖ It is very versatile and can be moulded into strong plastic items such as gearwheels.
❖ PET [polyester] made from a dicarboxylic acid monomer and diols (alcohol with an -OH functional
group).
❖ Forms ester linkage.
❖ It can be found in a wide variety of packaging for both food and drink, as well as in clothing fibres.
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Comparing addition and condensation polymerisation
Addition polymerisation
monomers
used
Condensation polymerisation
▪
usually many molecules of a single ▪
monomer
▪
monomer is unsaturated, usually
contains a C=C double bond
▪
molecules of two monomers usually
used
monomers contain reactive functional
groups at ends of each molecule
reaction
taking place
an addition reaction, monomers join
together by opening the C=C double
bond
condensation reaction with loss of a small
molecule each time a monomer joins the
chain
nature of
product
▪
only a single product - the polymer
▪
two products -the polymer plus water
▪
non-biodegradable
▪
can be biodegradable
▪
resistant to acids
▪
PET can be hydrolysed back to
monomers by acids or alkalis
Natural polymers (proteins)
❖ Proteins are built from amino acid monomers
❖ There are 20 different amino acids used and they each contain two functional groups: an amino
group (-NH2) and a carboxylic acid group (-COOH)
❖ When this is repeated many times using the different amino acids, a polymer is formed.
❖ Short polymers (up to 15 amino acids) are known as peptides. Longer chains are called
polypeptides or proteins.
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Plastics
❖ Plastics can be moulded or shaped under heat and pressure.
❖ extremely strong but low-density: soft-drinks bottles.
❖ Low conductivity: heat-retaining products, including food containers and insulating foam.
❖ very flexible: items ranging from plastic bags to garden hoses.
❖ used in 3D printing, the production of respirator masks and the creation of prosthetic limbs.
Environmental challenges
❖ Pollution problems from plastics:
➢ choke birds, fish and other animals that try to eat them.
➢ they clog up drains and sewers and cause flooding.
➢ they collect in rivers, and get in the way of fish. Some river beds now contain a thick layer of
plastic
➢ they blow into trees and onto beaches, the place looks a mess.
❖ Adaptation of usage in the following ways:
➢ to reduce the level of plastic packaging wherever possible
➢ to avoid the use of ‘single-use plastic'
➢ to reuse and recycle wherever possible.
❖ Incineration can be used to burn plastic waste, although care must be taken not to release toxic
fumes into the air.
❖ Disposal in landfill sites suffers from the problem that most plastics are not biodegradable.
❖ Plastics that are biodegradable causes the problem of degradation products leaching into the
groundwater.
❖ The pollution arises in the form of microplastics which take the form of nurdles and microbeads.
❖ Nurdles are pre-production plastic pellets and resin materials, serve as raw material in the
production of plastic products.
❖ Microbeads are the much smaller plastic spheres found in cosmetic facial scrubs, shower gels and
toothpastes.
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