Classifcation of organic compounds

Organic compounds can be classified into aliphatic and aromatic compound depending on their molecular  structure which is the way atoms are arranged in the molecules.
 
Aliphatic compounds

compounds whose molecules are composed of chains of carbon atoms are known as aliphatic compounds.
There is no limit to the number of carbon atoms in a given chain. Often, a given carbon chain may even have one or more branches. Some examples of aliphatic compounds are

1. peptane(a straight chain compound), and 
2. 2-methylbutane(a branched chain compound).

Such straight and branched chain aliphatic compounds are called acyclic compounds
In the actual molecular structure, the carbon chains are not in truly straight lines as is conveniently represented on paper. Instead, the chains are zig-zag  lines because of the tetrahedral nature of the carbon bonds

Sometimes, the end carbon atoms of an open aliphatic chain can also join together to form a closed system or rings as in cyclopropane and cyclohexane.Such  compounds  are know as cyclic compounds



Aromatic Compounds
 
Aromatic compounds are a special class of cyclic compounds based on benzene, C6H6, a 6-carbon ring compound. All other aromactic compounds are derivatives of benzene, .e.g. pheylamine(aniline) and phenol. Some derivatives may also contain straight carbon chains as side chains. The following are some examples of aromatic compounds.

Hydro Carbons

Hydro carbons are one of the simplest organic compounds because they are called they are composed of just two element only, which is carbon and hydrogen. All hydrocarbon have the molecular formula C_xH_y, where x and y represent positive whole numbers. Some examples are methane, CH₄, (x=1, y=4) hexane C₆H₁₄ (x=6, y=14). They are further divided into two main groups which are the aliphatic hydrocarbons and the aromatic hydrocarbons, depends on their structure.

Hydrocarbon can be gotten naturally from coal, natural gas and petroleum. These are often known as fossil fuels because they are; the remains of plant and animals that died millions if years ago and; used mainly as fuels, that is burnt to release heat or other forms of energy.
 Coal, petroleum and natural gas are solid, viscous liquid and gaseous fuels respectively.

basic rules for naming orgaic compounds

Aliphatic organic compounds can be named by following these basic rules

1.  Take the longest  continuous carbon chain as the root hydrocarbon  and name it according to the number  of carbon atoms it contains, adding the appropriate suffix to indicates the principle substituent group
2. Number the carbon atoms in the root hydrocarbon from the end which will give the lowest number to the suffix, and then the prefix(es).
3. Indicate the other substituent by prefix preceded by numbers to show their positions on the carbon chain.
4. When two different alkyl groups are substituted to one organic compounds, they should be names based on the one that come first alphabetically e.g. 2-methylbuatne.

For example let's follow this step by step. In other to name correctly an aliphatic compound let’s say for example 2-methylbutane. The first step is to count the number of carbon atoms in such a way as to give the alkyl group substituted the least possible number.
From the diagram above of the structural formula of the aliphatic compound, it is either you name it 3-methyl butane or you name it 2-methylbutane, but the former is wrong. This is because you will have to give the lowest possible number to carbon carrying the alkyl group. If you start to count form your left you will name it 3-methylbutane. This is because methyl is attached to the third carbon atom. But if you start from the left you will have to name it 2-methylbutane which is the correct naming.
It doesn't really matter whether you start from your left or right just make sure that you name it with the lowest possible number.


Let us see another example.
 3-ethylHexane.

In this case we will start to count from the left so that the alkyl group can be given the lowest possible number. If you have already noticed if we start from the left we will have to give the ethyl the number 3 while if we start from the right we will have to give the ethyl the number 4. Since we are looking to give it the lowest number we will have to start form the left. it is that simple.

All you have to do is to remember to count from the left and from the right then you decide which has the smaller number, and then use it.