Introduction to Organic Chemistry | GCE O Level

Organic chemistry is the subject which involves the properties, structure, reactions, and preparation of carbon-containing compounds.

These compounds can be hydrocarbons and other compounds containing elements such as nitrogen, hydrogen, halogens, sulfur, silicon and oxygen.

However, carbon dioxide (CO2), carbon monoxide (CO) and calcium carbonate (CaCO3) are some compounds containing carbon but they are not classified as organic compounds.

This is because organic molecules do not only include carbon. They contain hydrocarbons or carbon bonded to hydrogen.

Organic chemistry has massive applications such as this study is used in pharmaceuticals, petrochemicals, explosives, food, paints, and cosmetics as well.

In this topic, you should be aware of the following topics:

1. Homologous series
2. Functional group
3. Fractional distillation of crude oil

Homologous series:

The alkanes, alkenes, carboxylic acids, alcohols and cycloalkanes are examples of homologous series.

A homologous series is a combination of chemicals which have similar chemical properties and they also have the same general formula. In other words, they can be represented by a general formula.

The members in a homologous series have the following charactersticks:

1. They show a gradual change in physical properties (such as boiling points).
2. They are represented by the general formula (a way to identify the molecular formula of the molecule, based on the number of carbon atoms it contains).
3. They can be made by similar methods of preparation.
4. Their chemical properties are the same.

The first homologous series is the alkanes and their name ends with -ane. They are insoluble in water and their general formula is CnH2n+2.

Before moving on, let’s discuss what is a functional group?

Functional group:

In organic chemistry, a functional group is a particular group of atoms or bonds (a group of atoms) in a compound that is responsible for the characteristic chemical reactions of that compound.

In other words, it is responsible for the characteristic properties of a compound.

It is to note that alkanes do not have any functional group (they only have C-C or C-H bonds). The functional group of alkenes is C=C (unsaturated hydrocarbons).

Moreover, the functional group of carboxylic acids and alcohols is -COOH and -OH respectively.

Alkenes are the second homologous series and their general formula is CnH2n. They are unsaturated hydrocarbons because they have carbon=carbon double covalent bonds.

You should also know that isomers are the compounds with the same molecular formula but different structural formula. Now, it is time to learn about the fractional distillation of crude oil and the uses of its fractions.

Fractional distillation of crude oil:

Petroleum is a mixture of organic compounds that are present in the depth of sea and soil. To separate crude oil into its constituent fractions (such as Naphta, Gasoline and Kerosene), fractional distillation is used.

The crude oil enters the tall fractionating column and as you go higher in this column, the hydrocarbons have a low boiling point, viscosity but higher flammability.

When the boiling point of a component is reached, it goes to the top of the column and in this way, all the constituents are gradually separated.

The uses of some petroleum fractions are:

1. Lubricating oil: For the manufacture of waxes and polishes and they also lubricate machines. The boiling point is 300 to 350°C.
2. Petroleum gas: It is mostly used as a fuel for heating and cooking. The boiling point of this fraction is around 40°C.
3. Naptha: It is usually used as a solvent. It is utilised in hydrocarbon cracking, laundry soaps, and cleaning fluids. It is also used as a raw material for plastics and detergents.

There are other fractions such as gasoline (as fuel for motorcars), kerosene (fuel for aircraft engines) and bitumen (to build highways, motorways and rail networks) and they are separated according to their boiling points.

Due to the competing uses of petroleum, biofuel is one fuel that can replace petroleum. Biodiesel (made from plant oils) and biogas (gas produced when organic matter decays) are some examples of biofuel.

Conclusion:

The topic, introduction to organic chemistry, requires you to know about the homologous series, functional group, general formula and the fractional distillation of crude oil.

Moreover, the uses of some of the petroleum fractions have been discussed as well. Thank you very much for reading and remember to practise plenty of past papers regarding this topic to make your concepts clear.