Question

What is IUPAC nomenclature? How are root words assigned according to IUPAC?

Answer 1

It’s a method of naming the organic compounds (compounds which are formed generally of carbon, hydrogen, nitrogen, oxygen, sulphur etc.) A longest number of carbon chains is selected firstly and named according to the group attached. Every group has its short form for example- $OH$ group ($ol$) is written after the chain name.

Complete step by step answer:
There are certain steps that we have to follow if we want to name any organic compound. You get better understanding if I take an example- $C{H_3} - C{H_2} - C{H_2} - C(C{H_3})(OH)({C_2}{H_5})$

Suppose we have this compound and we don’t know its exact name so, the first step is to select a carbon chain which is the longest. When we try to write this above compound in long form, we get to know that the last carbon contains three groups: a $- C{H_3}$ group, a $- OH$ and a $- {C_2}{H_5}$ group.

So firstly we take the longest chain which is of six carbon atoms and according to this six carbon system is known as “hex-“. If there is one carbon atom we will write it as methyl, if there are two carbon chain ethyl is written for it, for $3,\,4,5,\,6.....$ carbons names are assigned as propyl, butyl, pentyl, hexyl… etc.

Now our next step is to choose the functional group, a functional group is the one containing atoms also other than carbon. Like $- OH$ as alcoholic group can be written as $ol$ after the carbon chain, $- CHO$ is aldehyde group named as $al$ after the carbon chain and also $R - CO - R$ which is a carbonyl group between two alkyl groups (R). There are many groups like these and other than the groups, there are double and triple bonds present between two carbons. For double bond$(ene)$ and for triple bond $(yne)$is written after the carbon chain.

Let’s get back to the example that we have taken. In this example a structure is given having six carbon atoms so, (hex) is taken and we have an alcoholic group $- OH$ at ${3^{rd}}$ carbon atom, so we will write it as $3 - hexanol$. Here (al) is attached with the longest carbon chain name. This example is a simple one, there are many organic compounds which have bulky groups and double and triple bonds then according to it naming is done.

Note: You can write the numbering of any functional group before the name and also in between the chain name. Both are correct according to IUPAC. So for the above compound if we write the numbering of the functional group before the carbon chain name, it will be $3 - hexanol$ and also if we write name before the name of the functional group, it will be like this $hexan - 3 - ol$.