An Introduction to
Organic Chemistry

The word Organic is one of the most overused in the English language. People use it as a derogatory term in phrases like Don't eat that; it's not organic. Of course, there is a precise scientific definition of the word. In science, Organic can be a biological or chemical term. In Biology it means any thing that is living or has lived. The opposite is Non-Organic. In Chemistry, an Organic compound is one containing Carbon atoms. The opposite term is Inorganic.

It's the Chemical meaning I want to explore in this essay.

All substances are made up of molecules which are collections of atoms. All the molecules in existence are made up of about a hundred different kinds of atoms.

For example, a water molecule is composed of two atoms of Hydrogen and one atom of Oxygen. We write its formula as H₂O.

A molecule of Sulphuric Acid contains two atoms of Hydrogen, one atom of Sulphur and four atoms of Oxygen. Its formula is H₂SO₄.

These are simple molecules containing only a few atoms. Most Inorganic molecules are small. Below are a few common inorganic substances with their formulas.

All of these molecules have less than a dozen atoms.

The symbols Ca, K, Mn, Na and Cl stand for calcium, potassium, manganese, sodium and chlorine.

Most atoms are only capable of forming small molecules. However one or two can form larger molecules. By far and away the best atom for making large molecules with is Carbon. Carbon can make molecules that have tens, hundreds, thousands even millions of atoms! The huge number of possible combinations means that there are more Carbon compounds that those of all the other elements put together!

A single Carbon atom is capable of combining with up to four other atoms. Sometimes a Carbon atom will combine with less.

The unique thing about the Carbon atom is that it will combine with other Carbon atoms.

This means that Carbon atoms can form chains and rings onto which other atoms can be attached.

This leads to a huge number of different compounds. Organic Chemistry is essentially the chemistry of Carbon

Carbon compounds are classified according to how the Carbon atoms are arranged and what other groups of atoms are attached.

The simplest Organic compounds are made up of only Carbon and Hydrogen atoms only. Even these run into thousands! Compounds of Carbon and Hydrogen only are called Hydrocarbons. The simplest Hydrocarbon is actually methane, CH₄.

As the reader can see, there is a series of these compounds with this general formula:

This series of compounds are called alkanes. The lighter ones are gases and used as fuels. The middle ones (7 Carbons to 12 Carbons) are liquids used in petrol (gasoline). The higher ones are waxy solids. Candle wax is a mixture of alkanes.

After Butane, the names of these compounds are from the Greek for the number of Carbon atoms followed by the suffix -ane. So, Decane would have the formula

Polythene is a very large alkane with millions of atoms in a single molecule. Apart from being flammable, alkanes are stable compounds found underground.

The alkanes are not the only hydrocarbons.

Another series of compounds are called the alkenes have a general formula:

The simplest alkenes are

• C₂H₄ (ethene - used as an industrial starter chemical)

• C₃H₆ (propene)

• C₄H₈ (butene)

• C₅H₁₀ (hexene)

These compounds are named in a similar manner to the alkanes except that the suffix is -ene.

A third series are the alkynes:

Examples are:

• C₂H₂ (ethyne - better known as acetylene which is used for welding underwater)

• C₃H₄ (propyne)

• C₄H₆ (butyne).

Alkanes, alkenes and alkynes all contain Carbon atoms in linear chains.

There are also hydrocarbons arranged in rings:

• C₆H₆ (benzene - an industrial solvent)

• C₇H₈ (toluene)

• C₁₀H₁₀ (naphthalene - moth balls).

When Oxygen atoms are added, the variety of compounds grows enormously.

General Formula	Series Name	Examples
CnH2n+1OH	Alcohols	CH3OH - methanol (wood alcohol) C2H5OH - ethanol (drinking alcohol)
(CnH2n+1)2O	Ethers	(CH3)2O - dimethyl ether (a gas) (C2H5)2O - diethyl ether (liquid used as an anaesthetic)
(CnH2n+1)2CO	Ketones	CH3COCH3 - dimethyl ketone (acetone: nail-varnish remover)
CnH2n+1CHO	Aldehydes	HCHO - Formaldehyde (preservative in labs) CH3CHO - Acetaldehyde
CnH2n+1CO2H	Fatty Acids	HCO2H - Formic Acid (ant bites / nettles) CH3CO2H - Acetic Acid (vinegar) C2H5CO2H - Butyric Acid (rancid butter)
RCO2R' (R, R' are CH chains).	Esters	CH3CO2CH3 - methyl methoate (pear drops)

An interesting phenomenon with organic molecules is called isomerism. Let us look at two compounds introduced above.

Dimethyl Ether: (CH₃)₂O and Ethanol: C₂H₅OH.

The first is a gas which will knock you out if inhaled. The other is common alcohol drunk in spirits. The two molecules are shown below.

Notice that both compounds contain 2 Carbon atoms, 6 Hydrogen atoms and 1 Oxygen atom.

Even though the atoms are the same, they are arranged differently. This yields two different compounds with the same number of atoms. These compounds are isomers.

Isomerism increases the number of Organic compounds. The more Carbon atoms in a compound, the more isomers exist.

Most organic compounds contain Nitrogen as well as Oxygen. Special Organic compounds can contain atoms like Phosphorus, Sulphur and even Iron (e.g. Haemoglobin).

As can be imagined, these additions increase the number of compounds. Apart from the naturally occurring Organic compounds, millions more can be synthesised. Examples of both are shown below.

There is no difference between the same substance extracted from living organisms and made in a laboratory.

I hope this introduction to Organic Chemistry indicates just how vast and interesting the subject is.