Naming a organic compound is a multi step process and should be done very carefully. But naming an alkane compound is the easiest in organic compound IUPAC nomenclature. When naming alkane, that includes selecting longest carbon chain, identifying substituents, numbering carbon chain properly and some other steps. We will discuss those steps in several examples to write IUPAC names of alkanes properly.
You can see every name in above example are finished with ane suffix. In the IUPAC nomenclature, names of alkane should be finished with ane suffix.
Also you see, another suffix (meth, eth, prop) is used in front of ane suffix. These meth, eth, prop suffixes say, how many carbon atoms are in the root chain (will explain latter in the tutorial) of the molecule. Also we call these meth, eth, prop, more are word roots.
Lets take one example (propane) to explain in detail.
In C3H8 molecule, there are three carbon atoms. Also there are only single bonds between carbon atoms (C-C). So this is an alkane and name should be finished as ane. Due to exist of three carbon atoms, prop suffix is used.
So final name is propane.
This is a simple thing. But we do this in several steps to understand well.
What is the IUPAC name of this alkane? CH3CH2CH2CH2CH2CH2CH3
Seven carbon atoms are in this alkane molecule. For seven carbon atoms what is the word root? heptane is the word root and IUPAC name is heptane.
Each steps are explained in detail below.
Identify longest continuous carbon chain (which includes maximum number of carbon atoms). It is called root chain. Then other carbon atoms which not included in root chain are defined as substituents or branched chains.
There are five carbon atoms in the root chain and two substituents in the below organic molecule.
Substituents are parts which are not included in main branch. Some substituents and their substituent names are noted below.
When writing IUPAC name, we first write substituents chain name and then root chain. Don't think about much in this level. You will understand more when examples are discussed.
In the above example, you can see two -CH3 groups are as substituent groups. According to the IUPAC names for substituents, methyl should be the name for -CH3 groups.
We do several examples to understand whether substituent groups are present or not and if they are present, what are the names we are going to applied.
You cannot separate carbon atoms to two or more carbon chains in this molecule. So there is only one carbon chain. Instead of carbon and hydrogen, no other element is combined. So there is no more substituents.
You can draw two carbon chains. You should select the main carbon chain to contain highest number of carbon atoms. Then other carbon part become a substitute chain (substitute group).
In the above molecule, methyl groups are attached to two different carbon atoms. You will understand now, attaching position is important in naming the molecule.
So how to give position?
Give numbers to the carbon atoms as 1,2,3,....
In the numbering, we can do it two ways. But,
This is the correct way to numbering.
This is wrong.
With substituent group names, their attached positions also should be given. in the example, two methyl groups are attached to 2nd and 3rd carbon atoms respectively. Due to two same substituent are attached, di suffix should be written after the positions-.
According to the number of carbon atoms in the root chain, final name should be finished. In this example, there are five carbon atoms in the root chain. So pent prefix is used and name should be finished with ane suffix.