IUPAC Naming

As Board exams are coming closer, we observed that students are getting anxious about their performance and results in the exams. With anxiety comes confusion and we tend to make silly mistakes, especially in chemistry, where it becomes difficult for the students to understand the basic concepts. IUPAC naming is a very structured topic. After analyzing previous years’ question papers, we found that at least one sure shot question is asked either directly or indirectly in the Board Exam from this topic. So, here, let’s try to understand the topic in depth.

We will start with a fundamental question: Why do we need a naming system at all?

  • Out of the 10 million plus compounds classified by humans, more than 9 million compounds are organic (carbon based).
  • Many of the organic compounds are given a common name like citric acid, which is found in citrus fruits. Still, naming all the compounds is an impossible task.
  • Can we follow the naming convention like the inorganic compounds. That has names formed by the constituent elements, like ZnSO4 as Zinc Sulphate. But in the case of organic compounds, same elements form in many different forms to make many different compounds. Like C and H alone makes, CH4, C2H6, C6H6 etc.

So, there is a need to differentiate between these compounds. If a name is given, then it should specify one compound and if a compound is given, then it should be named uniformly by all.

Summary of IUPAC naming convention

Let’s start with identifying the longest chain of the compound

Longest Chain

Naming word

C Meth

C-C Eth

C-C-C Prop

C-C-C-C But

C-C-C-C-C Pent

C-C-C-C-C-C Hex

C-C-C-C-C-C-C Hept

C-C-C-C-C-C-C-C Oct

C-C-C-C-C-C-C-C-C Non

C-C-C-C-C-C-C-C-C-C Dec

Now let’s identify the functional groups of the compound.

Functional Group name

-OH -ol

-COOH -oic aid

-COOR -alkyl…oate

-COCl -oyl chloride

-CONH2 -amide

-CN -nitrile

-CHO -al

=CO -one

-NH2 -amine

-F Fluro-

-Cl Chloro-

-Br Bromo

-I Iodo

Identify the parent functional group by the preference order as given in the table above.

And now, identify the double triple bonds in the chain

bond name

C-C -ane

C=C -ene

C☰C -yne

Identify any side chains and find its name, as per the rules given above.

Number the longest chain such that the position numbers of functional groups and double / triple bonds are as low as possible. If the compound can be specified without specifying the number, then, the number need not be specified.

Let us take a simple example to show:

CH3-CH2-Cl

Naming Word: Eth
suffix: ane
Functional group: Chloro

Functional group position: not required, as only one possible location.
Name is: Chloro ethane

CH3-CH2-CH2-Cl

Naming word: Prop
suffix: ane
Functional group:: Chloro

Functional group position: 1
Name: 1-Chloro propane

CH3-CH(Cl)-CH3

Naming word: Prop
suffix: ane
Functional group:: Chloro

Functional group position: 2
Name: 2-Chloro propane

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