What is Organic Chemistry?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.MoleculesAll 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.
Molecules With CarbonMost 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. We say it has a valency of 4. Sometimes a Carbon atom will combine with fewer atoms.
In other words Carbon combines 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.
HydrocarbonsThe 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.Please note that the molecule structure images below show the structure of three dimensional molecules in two dimensional format.
AlkanesThe simplest Hydrocarbon is methane, CH4. This is the simplest member of a series of hydrocarbons. Each successive member of the series has one more Carbon atom than the preceeding member. This is shown in the table below.
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. In the alkanes, all four of the Carbon valency bonds are taken up with links to different atoms. These types of bonds are called single bonds and are generally stable and resistant to attack by other chemicals. Alkanes contain the maximum number of Hydrogen atoms possible. They are said to be saturated. The alkanes are not the only hydrocarbons.
AlkenesAnother series of compounds is called the alkenes. These have a general formula:
Alkenes have fewer hydrogen atoms than the alkanes. The extra valencies left over occur as double bonds between a pair of Carbon atoms. The double bonds are more reactive than single bonds making the alkenes chemically more reactive. The simplest alkenes are listed in the table below:
These compounds are named in a similar manner to the alkanes except that the suffix is -ene.
AlkynesA third series are the alkynes. These have the following formula:
Alkynes have two carbon atoms joined by a tripple bond. This is highly reactive making these compounds unstable. Examples of alkynes are:
These highly reactive substances have many industrial uses. Again the naming of these compounds is similar to the alkanes except that the suffix is -yne.
Carbon RingsAlkanes, alkenes and alkynes all contain Carbon atoms in linear chains. There are also hydrocarbons arranged in rings. Some examples follow:
When rings are combined with chains, the number of hydrocarbons is virtually infinite. And we are still using only two types of atoms (Carbon and Hydrogen). We will now add a third.
Carbon, Hydrogen and OxygenWhen Oxygen atoms are added, the variety of compounds grows enormously. In the table below, each row discusses a series of compounds.
In the above examples, each molecule has a single functional group. It is possible to have two or more functional groups on a molecule. These can be the same group (as in Oxalic Acid - a poison found in rhubarb leaves - which has two fatty acid groups) or different (as in Hydroxymethanoic Acid - which has a hydroxyl group and a fatty acid group):
 This shows how varied and complex even simple organic compounds can be. Sucrose has a pair of rings: one hexaganol, the other pentaganol. Each ring contains an Oxygen atom. The rings are joined by an Oxygen (Ether) link. The entire compound contains several Hydroxyl (OH) groups.
IsomerismAn interesting phenomenon with organic molecules is called isomerism. Let us look at two compounds introduced earlier.Dimethyl Ether: (CH3)2O and Ethanol: C2H5OH. The first is a gas which will knock you out if inhaled. The second 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 and the phenomenon is called Isomerism. In this example, the two molecules have different functional groups. They are structural isomers. Other types of isomers exist. Isomerism increases the number of Organic compounds. The more Carbon atoms in a compound, the more ways of arranging the atoms and the larger number of isomers.
Adding NitrogenMany very important organic compounds contain Nitrogen. This produces more series of compounds.
A famous compound containing Nitrogen is Trinitro Toluene (C6H2CH3(NO2)3 - usually abbreviated to TNT). This is an artificially made explosive. Its structure is shown below:
Other AtomsThe vast majority of organic compounds contain Carbon, Hydrogen, Oxygen and Nitrogen. Other types of atoms can be included to form even more compounds. These can contain atoms like Phosphorus, Sulphur (e.g. Thiamine, Vitamin B1), Magnesium (e.g. Chlorophyll) and 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. These can include atoms like Chlorine (used in pesticides). Examples of organic compounds containing Chlorine are shown below. There is no difference between the same substance extracted from living organisms and made in a laboratory.
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