ORGANIC CHEMISTRY NOTES:

Organic chemistry is the scientific study of the structure, properties,

composition, reactions, and synthesis of organic compounds that by definition
contain carbon.
Organic compounds are molecules composed of carbon and hydrogen, and may contain any
number of other elements.

THE CARBON CYCLE:

Carbon cycle portrays the movement of carbon in elemental and combined states on earth. 
Steps of a carbon cycle:

1. Carbon present in the atmosphere is absorbed by plants for photosynthesis.

2. These plants are then consumed by animals, and carbon gets bioaccumulated into their
bodies.
3. These animals and plants eventually die, and upon decomposing, carbon is released
back into the atmosphere.
4. Some of the carbon that is not released back into the atmosphere eventually become
fossil fuels.
5. These fossil fuels are then used for man-made activities, which pumps more carbon back
into the atmosphere.
Unique properties of carbon:

Carbon is a versatile element and is found in many different chemical compounds, including those
found in space. Carbon is versatile because it can form single, double, and triple bonds. It can also
form chains, branched chains, and rings when connected to other carbon atoms.
The two characteristic features seen in carbon, that is, tetravalency and catenation, put together give
rise to a large number of compounds. Many have the same non-carbon atom or group of atoms
attached to different carbon chains.
 Catenation: The property of forming long chains by self-linking with other carbon atoms to
form long chains, rings, double or triple bonds is called catenation.
 Isomerism: Compounds with same molecular formula but different structural formula are
called isomers. An isomerism commonly seen is due to difference in the arrangement of atoms or
groups of atoms & is called structural isomerism. The 4 types of structural isomerism are:
  Chain isomerism
  Position
  Functional
 Metamerism
 Tetravalency: Carbon has 4 electrons in its valence shell. Energy considerations do not
allow it to gain or lose 4 electrons; therefore it forms covalent bonds with other elements to
complete its octet. This accounts for its tetravalency and explains its ability to form a variety of
compounds.

HYDROCARBONS:

Compounds made up of only carbon and hydrogen atoms

• Organic chemistry: occurs in living organisms

• Mainly obtained from petroleum, natural gas, or coal
• Used in drugs, dyes, and solvents for paints
• Important source of energy
Saturated hydrocarbons

• Only contain C bonds

• All are alkanes (have single bond)
• These compounds have the maximum number of hydrogens that can be bonded to a
carbon

Unsaturated hydrocarbons

• Have multiple bonds: further classified as

o double bonds (alkenes)

o triple bonds (alkynes)

Bromine water test:

Unsaturated hydrocarbon: bromine water is decolourised

Saturated hydrocarbon: bromine water remains orange/yellow

Fractional distillation is a process by which the hydrocarbons in crude oil are separated
into useful components based on their boiling points.
Nomenclature

To name an organic compound:

1. Root word

• Depends on the number of carbons present in the carbon chain

# of Carbons Prefix # of Carbons Prefix

1 Meth- 6 Hex-
2 Eth- 7 Hept-
3 Prop- 8 Oct-
4 But- 9 Non-
5 Pent- 10 Dec-

2. Suffix

• Represents the nature of the bond in the carbon chain

• Single bond: -ane (alkane)

• Double bond: -ene (alkene)
• Triple bond: -yne (alkyne)
• OH present: -anol (alcohol)
• COOH present: -anoic acid (carboxylic acid)

3. Prefix

• Includes the functional group present & its position in the carbon chain
- Carbon chain: numbered from left to right/ right to left depending on which way
that:
1. Functional group gets the least number possible
2. Alkyl group gets the least number possible
HOMOLOGOUS SERIES

• A family of organic compounds containing the same functional group.

• They can be represented by a general formula, and each member of the series
differs from the next by a single -CH2 group.

• The members of a particular homologous series show similar chemical properties,

but gradually changing physical properties.

1) ALKANES:
• AKA saturated hydrocarbons because all 4 valencies of carbon are satisfied by the
general formula
• Only forms from single bonds between carbon molecules
• Generally unreactive

PREPERATION

• General formula: CnH2n+2

• Obtained from petroleum (main source of alkanes)

Method of Preparation:

1) FRACTIONAL DISTILLATION

Crude oil is separated into fractions by fractional distillation. The fractions at the top
of the fractionating column have lower boiling points than the fractions at the
bottom. All of the fractions are processed further in other refining units.

2) ADDITION REACTION WITH ALKENES

• When an alkene undergoes an addition reaction with H2, an alkane is formed

C2H4 + H2 = > C2H6

Physical Properties:

• Lower the carbon atoms, lower the boiling point

o Gases have lower boiling points than solids
• Lower the number of carbons, lower the melting point
• As the number of carbons increase, solubility decreases
• As the number of carbons increase, the density increases

Chemical Properties

Complete Combustion

 Main use of alkanes is combustion to release thermal energy

• Combustion is the oxidation of carbon compounds by oxygen in air to form
CO2 if there is a sufficient amount of oxygen
 When plenty of oxygen or air is present => creates carbon dioxide and water

C3H8 + 5O2 = > 3CO2 + 4H2O

Incomplete Combustion

 When not enough oxygen is present => creates carbon monoxide and water

2C3H8 + 7O2 = > 3CO + 8H2O

Substitution Reaction

 When you substitute the hydrogens in a compound with chlorine, bromine, and
iodine

3) ALKENES
 Alkenes are hydrocarbons
 This leads to a homologous series with the general formula CnH2n
 When carbon forms compounds each carbon atom always forms four bonds. This does not,
however, mean that each carbon is joined to four other atoms. It is possible to have bonds
grouped into pairs. These are called double bonds.
 Alkenes contain carbon atoms joined by double covalent bonds.
  They are unsaturated and are reactive

Preparation: CRACKING

CRACKING is a large industrial process which turns longer length molecules into shorter
length molecules (due to the high demand for petrol) by heating molecules with high
temperatures. This causes some of the carbon bonds to break and shortens the length of the
compound => producing alkenes
• Breaks down compounds into one alkane & one alkene
• Smaller compounds => lower boiling points => easier to ignite => more useful as fuels
• Example of equation: C10H22 => C8H18 + C2H4

Testing for Alkenes:

Bromine test: compound reacts with bromine and colour turns from brown to colourless

Physical Properties:

• Nature: Much more highly reactive than alkanes

• Solubility: soluble in most organic solvents other than water
• State: All alkenes except for ethene are colourless/odourless
• Melting and Boiling: Alkenes have higher melting points than corresponding alkanes
• The double bonds in alkenes are stronger than single bond in alkanes
• More the C & H atoms increase, higher the boiling & melting points

Chemical Properties:

• Addition Reaction:
• HYDROGENATION: Adding hydrogen to alkenes to give alkanes as products
o C2H4 + H2 = > C2H6
• HALOGENATION: Adding halogens to alkenes to give haloalkanes as products
o C2H4 + Br2 = > C2H4Br2
• HYDRATION: Adding water molecules to alkenes to give alcohol as products
o C2H4 + H2O = > C2H5OH
 o
• Polymerization
• When 2 or more molecules of the same compound associate to form a bigger
molecule

4) ALCOHOL
- Organic compound in which an hydroxyl functional group (-OH) is attached to a saturated
carbon (alkane)
• General formula: CnH2n+1OH

Preparation:

• Fermentation of Sugar
• Glucose produces alcohol and carbon dioxide
• C6 H12O6
• Ethanol is produced
• Addition reaction with alkenes : hydration
• When water/steam is added to an alkene, an alcohol is formed
• C2H4 + H2O = > C2H5OH

Physical Properties

• Colorless liquids with faint odor and burning taste

• Nature: inflammable volatile liquids
• Boiling & melting point: increases with increase in molecular weight
• Solubility: soluble in water as well as in organic solvents
• First few are very useful solvents (eg: especially ethanol will dissolve many
compounds which water can’t )
• Density: ethanol is lighter than water
• Very toxic

Chemical Properties

• Combustion
• Incomplete and complete combustion (find above)
o difference: alkanes are replaced by the corresponding alcohol
• Esterification
• Acetic acid + alcohol => ester + water
 • When carboxylic acids react with alcohols

 Esters: used in food flavourings and perfumes

o C2H2OH + CH3COOH = > CH3COOC2H5 + H2O
o CH3COOH is acetic acid => this reacts with every single alcohol in
esterification
 How to create products for esterification
o CH3 group goes first
o COO group goes second
o Alkane goes third

5) CARBOXYLIC ACIDS:
• Organic compound which contains the carboxyl group –COOH that is added to an alcohol
part
• Weak organic acids
• General formula: CnH2n+1COOH

Preparation:
• Oxidation of alcohols
 Alcohol + oxygen => carboxylic acid + water
 C2H5OH + O2 = > CH3COOH + H2O
 How to create the products of oxidation of alcohols:
o First Subtract CH2 from the product
- C2H5 = > CH3
- CH3 = > H
o Second: COOH group

Physical Properties:

• Odour: Pungent smell (smell of vinegar)

Chemical Properties:

• Reacting with an alkali or base to form salt and water

PETROLEUM: A FOSSIL FUEL:

The fossil fuels are petroleum (or crude oil), coal, and natural gas. They are called fossil fuels
because fossil fuels because they are the remains on plants and animals that lived a million years ago

Petroleum is a smelly mixture of hundreds of different compounds. They are organic compounds,
meaning they contain carbon and usually hydrogen. In fact most are hydrocarbons.

• Non-renewable because as petroleum is still forming, very slowly under the oceans and we
are using petroleum a lot faster than it can form, so it might eventually run out one day.

How do we use petroleum?

1. Half the petroleum pumped from oil wells is used for transport
2. Rest are burned for heat in factories, homes and power stations. For eg. Heat is used to turn
water into steam, to drive turbines
3. A small percentage is used as the starting chemicals to make other things: plastics, shampoo,
paint, thread, fabric, detergents, makeup, medical drugs, and more.

Refining Petroleum: Fractional Distillation

Petroleum contains hundreds of different hydrocarbons. All of this isn’t very useful. So the first
step is to separate the compounds into groups with molecules of a similar size.

Refining petroleum in the lab

Materials:

• Thermometer
• Pear-shaped flask
• Petroleum (crude oil)
• Bunsen burner
• Test tube
• Watch glass

Procedure:

1. Heat the petroleum, so the compounds start evaporating. The ones with smaller molecules
go first, since it takes less energy to free these from the liquid
2. As the hot vapours rise, so does the thermometer reading. The vapours condense in the cool
test-tube.
3. Once the thermometer reading reaches 100 degrees, replace the first test tube with an
empty one. The liquid in the first test-tube is your first fraction from the distillation
4. Collect three further fractions in the same way, replacing the test-tube at 150 degrees, 200
degrees and 300 degrees.
 5. Compare the fractions (how runny they are how easily they burn etc.). You can burn the
samples on a watch glass

END RESULT: TRENDS:

The larger the molecule in a hydrocarbon:

• The higher its boiling point

• The less volatile it will be
• The less easily it will flow
• The less easy it will burn.

**The trends help dictate what the fractions will be used for**

In the petroleum factory

In a refinery, the fractional distillation is carried out in a power that is kept very hot at the base, and
cooler towards the top

Petroleum is pumped in the base. The compounds start to boil off. The ones with the smallest
molecules boil first, and rise to the top of the tower

As the molecules become larger, the fractions get less runny, or more viscous.

Cracking hydrocarbons

Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient as they
do not flow easily and are difficult to ignite. Crude oil often contains too many large
hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand. This is
where cracking comes in.

Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful
hydrocarbon molecules. Fractions containing large hydrocarbon molecules are heated
to vaporise them. They are then:

 heated to 600-700°C
 passed over a catalyst of silica or alumina
These processes break covalent bonds in the molecules, causing thermal
decomposition reactions. Cracking produces smaller alkanes and alkenes.

Cracking of decane

There is a greater demand for smaller hydrocarbons than larger ones.

decane → octane + ethene

C10H22 → C8H18 + C2H4

The process is as follows:

Some of the smaller hydrocarbons formed by cracking are used as fuels (eg large chains are
often cracked to form octane for petrol, which is in high demand), and the alkenes are used to
make polymers in the manufacturing of plastics. Sometimes, hydrogen is also produced during
cracking.