Organic Chemistry

Compound Names

Organic chemistry deals with 3 types of organic (carbon-containing) molecules in IGCSE:

• Alkenes
• Alkanes
• Alcohols

All 3 groups of molecules contain carbon and hydrogen atoms. However, their structures are slightly different. Each molecule from these groups is named using a prefix that denotes the number of carbon atoms and a suffix that identifies the homologous series.

• Alkene: ene
• Alkane: ane
• Alcohol: anol

Only the names of the first 4 molecules of each group need to be known for IGCSE.

Methene does not exist because it is impossible for a single carbon atom to form double bonds with itself.

Homologous Series

Homologous series are a family of compounds with the same general formula and similar chemical properties. Compounds in the same homologous series:

• have the same functional group
• have the same general formula
• have similar chemical properties
• display a trend in physical properties

Alkenes have double bonds because they are unsaturated (more carbon-hydrogen single bonds can be accomodated for). Alkanes are saturated with hydrogen atoms. Alcohols have a hydroxyl group attached to an alkyl group, meaning they are not hydrocarbons (due to the presence of an oxygen atom).

Alkenes

An alkene is an unsaturated hydrocarbon that contains 1 carbon-carbon double covalent bond.

Cracking

Cracking is the process of breaking down larger alkane molecules into smaller alkene molecules and either an alkane molecule or a hydrogen molecule.

Alkanes

An alkane is a saturated hydrocarbon that only contains single covalent bonds. Alkanes are less reactive than alkenes because they are saturated.

Fuels

Fractional Distillation of Petroleum

Petroleum is a mixture of hydrocarbons with different boiling points. These hydrocarbons can be separated into fractions in a fractionating column.

The temperature is not the same throughout the furnace.

• The bottom of the furnace is hot, so only the fraction with the highest boiling point (bitumen) can remain a liquid
• The top of the furnace is comparatively much cooler, so only the fraction with the lowest boiling point (refinery gas) can boil

The different fractions have different uses.

• Refinery gas: Gas used in cooking and heating
• Gasoline: fuel used in cars
• Naphtha: a chemical feedstock
• Kerosene: jet fuel
• Diesel oil: fuel used in diesel engines
• Fuel oil: ships and home heating systems
• Lubricating oil: waxes, polishes, and lubricants
• Bitumen: making roads

Fractions of petroleum are separated according to their boiling points.

1. Petroleum is heated and vapour rises
2. Vapour cools down as it rises through the furnace
3. Fractions condense when the vapour reaches their boiling points

Polymer

A polymer is a long chain molecule formed from small repeating units called monomers.

Addition Polymerisation

The addition of multiple monomer units results in an addition polymer. Addition polymers have the poly prefix attached to the name of the monomer. For example, poly(ethene) is an addition polymer made from multiple ethene molecules.

The orientation of each monomer does not matter as long as they have the same chemical structure and formula.

Condensation Polymerisation

Nylon is an example of a condensation polymer. Condensation polymerisation forms a polymer and a small molecular waste product while addition polymerisation only produces a polymer.

Nylon is made from a dicarboxylic acid (a carboxylic acid with two carboxyl -COOH groups) and a diamine (an amine with two amine -NH2 groups).

1. the dicarboxylic acid loses a hydroxyl group (-OH) from each carboxyl group (-C(=O)OH)
2. the diamine loses one hydrogen (-H) from each amine group (-NH2)
3. the hydrogen and hydroxyl combine to form water
4. the remainder of the dicarboxylic acid, now -(O=)C-R-C(=O)- and the remainder of the diamine, now -(H)N-R-N(H)- combine to form a condensation polymer [-(O=)C-R-C(=O)N(H)-R-N(H)-]_n

1. the dicarboxylic acid loses a hydroxyl group (-OH) from each carboxyl group (-C(=O)OH)
2. the diol loses one hydrogen (-H) from each hydroxyl group (-OH)
3. the hydrogen and hydroxyl combine to form water
4. the remainder of the dicarboxylic acid, now -(O=)C-R-C(=O)- and the remainder of the diol, now -O-R-O- combine to form a condensation polymer [-(O=)C-R-C(=O)O-R-O-]_n

Proteins are natural polyamides. These are formed by the condensation polymerisation of amino acids, H2N-CHR-COOH (where R is any side chain), rather than dicarboxylic acids and diamines.

While the structure of a synthetic polyamide like nylon looks like this: [-(O=)C-R-C(=O)N(H)-R-N(H)-]_n
The structure of a polypeptide (protein) looks like this: [-(H)N-R-C(=O)N(H)-R-C(=O)-]_n
Notice how each monomer unit in a protein has the remanence of an amine group and of a carboxyl group.