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ORGANIC CHEMISTRY NOTES
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Each family of organic compounds forms what is called a homologous series
...
The result is a huge variety of 'organic compounds' which can
be classified into groups of similar compounds i
...
different homologous series
...
e
...
These days most
organic compounds are synthesized from raw materials, in particular the physical separation and
chemical manipulation of the products of crude petroleum oil
...
g
...

Members of a homologous series have similar physical properties such as appearance,
melting/boiling points, solubility etc
...
g
...

The molecular formula represents a summary of all the atoms in the molecule e
...
butane is
C4H10
...
g
...
Examples of functional
groups include:
o the double carbon-carbon bond C=C in alkenes,
o the oxygen-hydrogen atom group of the -OH in alcohols,
o and the group of four atoms constituting the -COOH group in carboxylic acids
...

They are referred to as 'saturated' hydrocarbons because they do NOT contain a double bond
and other atoms cannot add to them
...





Alkanes are a group of hydrocarbon molecules in which all the carbon and hydrogen atoms
are only joined by single covalent bonds (e
...
C-H or C-C)
...
The much larger alkanes are colourless liquids and the biggest
members of the series are white waxy solids
...

(1) is the molecular formula: a summary of the totals of each atom of each element in one
molecule
(2) is a 'shorthand' version of the full structural formula
(3) is called the structural formula: it shows how all the atoms are linked by covalent bonds the
dashes!
(4) is a '3D' representation of the structural formula (3) showing the spatial arrangement of the
atoms
...
ane
...
After these four preserved 'old trivial' names, the name is 'numerically'
systematic e
...
C5 carbon chain pentane; C6 chain hexane, C7 chain heptane, C8 chain
octane, C9 chain nonane, C10 chain decane etc
...




E
...
pentane
is linear or unbranched
...




E
...
3-ethylpentane
is branched, because it has an
'ethyl branch' from the 3rd carbon atom in the main chain
...

o The 3- denotes the position of the carbon chain branch i
...
the lowest number possible
for the start of the side-chain
...
g
...
for the associated carbon atoms in the main chain, where the 1st carbon
atom in the chain is considered as C atom 1
...
g
...
and ethyl
...
,
they are written out in alphabetical order (BUT di, tri are ignored in using this rule)
...

Follow the sequence of bullet points down, and then back up, so you are quite clear on the
relationship between all the structural and formula styles
...
It derives from an
elemental analysis of a compound
...
g
...

The molecular formula summarises all the atoms in the molecule BUT does not show their
arrangement at all
...

o Note that for propane, the empirical formula is identical to the molecular formula BUT for
2-methylpropane and butane, they are not identical
...

o Note also, that the molecular formula, does NOT distinguish the two structural isomers
butane and 2-methylpropane ('methylpropane')
...

An 'abbreviated' or 'shortened' structural formula is unambiguous if you know how to
interpret it! It shows how groups of atoms are linked or sequenced in a molecule
...
e
...

o

propane

o

or

2-methylpropane

butane
or
Note that methylpropane and butane can now be distinguished, BUT, you must be able
to envisage these correctly into a full structure that shows how all the atoms are
'connected', and this is explained next
...
e
...

o
o



o

propane

Page 4 of 20

2-methylbutane

Butane
You can use a mixture of styles of the abbreviated/structural/graphic/displayed formulae
...
g
...
e
...
The different molecules are known as ISOMERS
...

The existence of isomers is one of the reasons why such a huge array of different
organic compounds exists
...
e
...

In order to analyse a molecular formula for its possible isomers, you need to know what
forms of isomerism can occur and then 'take the molecular formula apart' and
reconstruct the atoms in as many different ways that seem possible
...

So, beware!, what seems different on 2D paper might not be in 3D reality, especially as
there is free rotation about single bonds, so using models for simpler molecules is
extremely useful at the start of studying isomerism
...


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

(2)
,2- methylbutane (2-methylbutane), volatile colourless liquid/gas,
oC, minimum branching
...
5oC, maximum branching
...


Equations for the complete combustion of a hydrocarbon
When a hydrocarbon molecule (reactant) burns in an excess of air-oxygen there are only two
products of the reaction
...

General word equation:
Hydrocarbon + oxygen ==> carbon dioxide + water
Word equations e
...
methane + oxygen ==> carbon dioxide + water
and the corresponding symbol equation is
CH4(g) + 2O2(g) ==> CO2(g) + 2H2O(l)
 Note that one CO2 for every C, and one H2O for every two H's in the hydrocarbon molecule
...



...
All the dashes represent the covalent bonds between the atoms in the molecules
...

Propane + oxygen ==> carbon dioxide + water
C3H8(g) + 5O2(g) ==> 3CO2(g) + 4H2O(l)
and in terms of displayed formula and balancing numbers
...
below)) and the new bonds formed
in the products (C=O and O-H)
...

for ethane the symbol equation is
...

C5H12(l) + 8O2(g) ==> 5CO2(g) + 6H2O(l)
The Incomplete Combustion of hydrocarbons






If there is not enough oxygen present to completely burn the fuel to carbon dioxide and water
other products may form causing pollution and fuel inefficiency
...

The most common partially burned products are likely to be carbon C (soot) and deadly
carbon monoxide CO
...
e
...
The soot, like any fine solid
'dust' is harmful when absorbed on the sensitive tissue of the linings of the nose, throat
and lungs
...
Coarse particles (10 microns) are
inhaled into your windpipe and settle there, causing irritation and more coughing
...

o Even very low concentrations of carbon monoxide can be fatal
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The bonding between oxygen and haemoglobin is quite weak to allow
easy oxygen transfer for cell respiration
...
The consequences are reduced blood oxygen
concentration leading to unconsciousness and eventually death!
There is also less heat released in incomplete combustion compared to complete
combustion since not all the carbon atoms of the fuel are fully combined with the maximum
amount of oxygen
...
g
...

 methane + oxygen ==> carbon + water
 CH4(g) + O2(g) ==> C(s) + 2H2O(l)
 for soot (mainly carbon) formation and
Page 7 of 20




methane + oxygen ==> carbon monoxide + water
2CH4(g) + 3O2(g) ==> 2CO(g) + 4H2O(l) for the formation of carbon monoxide

Methane and chlorine


Substitution reactions happen in which hydrogen atoms in the methane are replaced one at
a time by chlorine atoms
...


This reaction takes place in the presence of UV light but not in darkness
...


The SEPARATION of the crude oil mixture into fractions and the USES of these fractions
A fraction is a mixture of a restricted boiling point range of molecules; they have a similar number of
carbon atoms and physical properties
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









Crude oil is a complex mixture of mainly hydrocarbon compound molecules
...
The
chemical properties of each substance in the mixture are unchanged
...

The crude oil is heated to vapourise it (evaporated or boiled)
...
e
...

The rest separate out according to their boiling/condensation point so that the highest boiling
fraction, i
...
the less volatile molecules with higher boiling points, tend to condense more
easily lower down the column
...

Note: Covalent chemical bonds like C-C or C-H are not broken in the process, only the
intermolecular force of attraction is weakened to allow the initial evaporation or boiling
...
The products are
smaller alkanes used for fuels (e
...
petrol or diesel) and alkenes which are used to make
polymers-plastics and other important compounds
...
Either way, it
means the vast majority of crude oil can be turned into useful products
...

o The cracking reaction is an example of thermal decomposition - a reaction that
breaks down molecules into smaller ones using heat
...
g
...
g
...

The equations below illustrate the process, small molecules are used to show the overall
molecular change clearly BUT in practice the 'starter' molecules are likely to be more those
shown in equations (3) and (4)
...

o



(1)
butane

ethane

ethene
...
carbon double bond (C=C) as well as single
bonds
...
The first two in the series are shown below and are colourless smelly gases
...
g
...

They are made from cracking crude oil in the petrochemical industry processes
(1) is the molecular formula: a summary of the totals of each atoms of each element in one
molecule; (2) is a 'shorthand' version of the structural or displayed formula (3); (3) is called the
structural or displayed formula: it shows how all the atoms are linked with the covalent bonds ethene
(1)

, (2)

, (3)
propene

(1)

, (2a)

, (2b)

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, (3)

(1)

butene

, (2)

Three important reactions of alkenes
(1) Addition of bromine: A test to distinguish between ALKANE and ALKENE
hydrocarbons











...

Bromine dissolved
in water or
trichloroethane
solvent forms an
orange
(yellow/brown)
solution
...

The alkane
solution remains
orange - no
reaction
...


Alkenes are
unsaturated
molecules, atoms
can add to them
via the C=C
double bond, so a
reaction occurs
...



...

propene + bromine
==> 1,2dibromopropane

(2) Alkenes can add hydrogen to form a saturated alkane molecule





H2
propene + hydrogen ==> propane

Alkenes will react
with hydrogen gas
over a nickel
catalyst 150oC
The reaction
process is used to
make margarine
from vegetable oils
...

The unsaturated hydrocarbons form a homologous series called alkenes with a general
formula CnH2n Unsaturated means the molecule has a C=C double bond to which atoms
or groups can add
...
ene
o ethene

o

C2H4 or
propene

o

 C3H6 or
butene



or

or

or
The alkenes are more reactive than alkanes because of the presence of the carbon=carbon
double bond
...





or

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

Examples of addition reactions are: with hydrogen under pressure and in the presence of a
nickel catalyst to form an alkane

o


+ H2 ==>
ethene + hydrogen ==> ethane

+ H2 ==>
 propene + hydrogen ==> propane
 Alkenes react by 'addition' with bromine and decolourises the orange bromine water
because the organic product is colourless, and this is a simple test to distinguish an alkene
from an alkane
...
The
process is called hydrogenation,
o and the change in an 'unsaturated' part of an oil molecule is
o -CH=CH- + H2 ==> -CH2-CH2o So producing a 'saturated' section in the molecule
...

o e
...
ethene + oxygen ==> carbon dioxide + water
o C2H4 + 3O2 ==> 2CO2 + 2H2O
o However, they are NOT used as fuels for two reasons
...
They are far too valuable for use to make plastics, anti-freeze and
numerous other useful compounds
...
They burn with a more smokey flame than alkanes due to less efficient and
more polluting combustion
...

 The formation of big polymer molecules called polyalkenes from small molecules called
alkenes
o



Poly(ethene) from ethene is a cheap but very useful plastic used for plastic bags and bottles
(old or commercial names: polyethylene, polythene and polyethene)
...
g
...

Page 13 of 20

o

The formation of PVC is shown below
...
So it is used for covering
electrical wiring and plugs
...

What is ethanol and how can we make it?
The 'alcohol' of the homologous series of alcohols!

What we call alcohol in everyday life is a substance whose chemical name is ethanol
...



Ethanol structure

o

or

or
Page 14 of 20

or

The first formula is the simplest formula to show the structure of ethanol and the last
image is the full graphic structural displayed formula of ethanol, i
...
it shows all the
atoms and the bonds linking them together in the molecule
...

Ethanol is used as a solvent, as a bio-fuel (can be mixed with petrol or used directly), and
used to make esters' as well as the 'potent' chemical present in alcoholic drinks!
o The % alcohol in wines, spirits and beer varies from 1-40%
...

o There are health and social issues about the medical and behavioural aspects of
alcohol consumption
...
Binge
drinking and alcohol dependency can cause major social problems both within a family
and for the wider community
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The raw materials are mixed with
water and yeast at just above room temperature
...
The sugars react to form ethanol and carbon dioxide
...
When the reaction is over the ethanol is
separated from the reaction mixture by fractional distillation to make a petrol additive fuel or
whisky!
o e
...
glucose == enzyme ==> ethanol + carbon dioxide
o C6H12O6(aq) ==> 2C2H5OH(aq) + 2CO2(g)
o The progress of the fermentation can be followed by measuring the density of the
fermented liquid with a hydrometer
...

o Ethanol, from a solution made from fermented sugar cane, can be concentrated by
fractional distillation
...
e
...

 C2H5OH(l) + 3O2(g) ==> 2CO2(g) + 3H2O(l) + heat energy from the exothermic
reaction
o The natural fermentation process would have discovered by accident after its products
were sampled and so beer has been brewed for thousands of years
...

Ethanol can also be produced by the reaction of steam and ethene (from oil cracking) in
the presence of an acid catalyst (Phosphoric acid)
...
g
...
g
...

The higher temperature and catalyst speed up the reaction and increasing pressure moves the
equilibrium to the right (side least gaseous molecules at 300 oC)
o ethene + water ==> ethanol
o CH2=CH2 + H2O ==> CH3CH2OH (or C2H5OH)
o









o
+ H2O ===>
Advantages and disadvantages of the two methods of making ethanol:
o Advantages of fermentation: It uses a cheap and renewable resource like sugar cane
(Brazil) and sugar beet
...


Page 15 of 20

Disadvantages of fermentation: slow reaction and made by an inefficient batch
process, poor quality product e
...
low aqueous concentration of ethanol
...
g
...
The alcohol must also be distilled from the
fermentation mixture, also a costly process
...

o Advantages of ethene route: A fast and efficient continuous process in the
petrochemical industry which produces a relatively pure product in bulk
...
g
...

o Disadvantages of ethene route: using a non-renewable finite resource of crude oil
...
It is the presence
of this functional group that gives alcohols their characteristic properties
...
g
...

o





or
or
All the alcohols are flammable colourless liquids with a characteristic 'pleasant'?
odour
...

The next three are propanol (3rd in series), butanol (4th in series) and pentanol (5th in
series), note their names also end in
...

o
o



o

propanol

o

butanol

o

or

pentanol
Reactions of alcohols
...
BUT it is
this oxidation of ethanol that results in alcoholic drinks turning sour (e
...
cider, wine) when
exposed to air
...

o ethanol + oxygen ==> ethanoic acid + water
o CH3CH2OH + O2 ==> CH3COOH + H2O
o
o

+ O2 ==>
+ H2O
This oxidation can also be done by heating the ethanol with a mixture of sulphuric
acid and potassium dichromate (VI) solution
...

Page 16 of 20



When burned, ethanol, like any alcohol, on complete combustion forms carbon dioxide and
water
Ethanol + oxygen ==> carbon dioxide + water
CH3CH2OH(l) + 3O2(g) ==> 2CO2(g) + 3H2O(l)



Ethanol can be dehydrated to ethene by passing the alcohol vapour over heated
aluminium oxide catalyst
...
g
...

Carboxylic acids and esters
Carboxylic acids are a group of organic compounds which have weakly acidic properties
...
They
react with alcohols (another organic series of compounds) to form organic compounds called
esters which are used as solvents and components in perfumes and food flavorings
...

The structures of the first three members are given below: Names end in
...

o methanoic acid (old name 'formic acid')

o

or
or
ethanoic acid (old name 'acetic acid', in vinegar)

o


or
or
propanoic acid (old name 'propionic acid')






or
or
ESTERS: Carboxylic acids react with alcohols to form members of another homologous
series called esters
...


o



+
+ H2O
sometimes more simply written as
CH3COOH + CH3CH2OH
CH3COOCH2CH3 + H2O
Page 17 of 20

Condensation polymerisation
Involves linking lots of small monomer molecules together by eliminating a small molecule
...



Nylon (a polyamide) is formed by condensation polymerisation, the structure of nylon
represented below where the rectangles represent the rest of the carbon chains in each unit
...
)
This is the same linkage (-CO-NH-) that is found in linked amino acids in naturally occurring
macromolecules called proteins, where it is called the 'peptide' linkage
...
)
This is the same kind of 'ester linkage' (-COOC-) found in fats which are combination of long
chain fatty carboxylic acids and glycerol (alcohol with 3 -OH groups, a 'triol')
...

o In the manufacturing process the polymer chains are made to line up
...

Three problems associated with using and disposing of Polymers or Plastics

1
...
e
...

o Land-fill sites are getting full and recycling isn't as easy as it may seem
...
e
...

2
...

o The toxic fumes cause deaths in house fires and controversial problems with alleged
inefficient waste incinerators as they will definitely cause environmental problems if
burned on waste tips!
3
...
BUT this should not prevent us from
trying and it would be beneficial to prolong the life of the finite crude oil reserves AND
reduce pollution and space in land-fill sites
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Page 18 of 20

At the moment, a lot may have to be sorted by hand - lack of automation makes
the sorting more costly
...
A company in Scarborough, England, is
collecting waste plastic
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and has a good working life because the material isn't biodegradable!
Clear soft drink bottles are made from PET (polyethene/polyethylene terephthalate)
which can be recycled as fibre-fill for pillows and carpets
...

 Energy costs are a big economic recycling factor; it’s not just about making
naturally occurring resources like oil last longer
...

New plastics are being developed which are more biodegradable or can be recycled,
so will the paper bag and cardboard package make a comeback? (in Ireland you have
to bring your own bag or buy one, and not necessarily a plastic one!), this isn't a
recycling process BUT it does reduce environmental pollution
...
These plastic
notes apparently have the advantage of being more difficult to forge and they last
longer
...

Ideally some recycled thermoplastics and scrap material from a plastic product
manufacturing process, can be heated and remoulded in the same process or another
product
...

 Less green, but useful purpose is to use scrap plastic as a fuel, but complete
incineration is not always easy to be efficient
...



o

o

o

o

o
o

o

o

air
chemically
coal
compounds
crust
distillation
evaporati
ng
flammable
fossil
fractional
fuels
gas
greater
higher
hydrocarbons
less
mixture
molecules
organisms
physical
pr
essure
sedimentary
similar
temperatures
two
unchanged
vis
cous
(1) Crude oil is extracted from the Earth’s
remains of marine
fuels
the action of heat and


...
The
, oil and natural

have formed by

over millions of years, in the absence of
Page 19 of 20

, on material from animals and plants (organic material) which has
been covered by layers of

rock
...
A mixture

consists of

or more elements or

not

combined together
...
This makes it possible to separate the substances in a mixture by
methods including distillation
...
They can be

separated into fractions, each of which contains molecules with a
number of carbon atoms, by

the oil and allowing it to condense at a

number of different


...


(4) The hydrocarbon molecules in crude oil vary in size
...
(a) the
its boiling point, (b) the

it flows and the more
the less
molecules as

volatile it is, (c) the less easily

it is, and (d) the less easily it ignites, meaning
it is, and this limits the usefulness of hydrocarbons with large

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