How to name organic compounds in chemistry
In chemistry, naming organic compounds somewhat becomes challenging for students especially when taking their baby steps in chemistry.
IUPAC nomenclature is divided into nomenclature in inorganic chemistry and organic chemistry.
The naming of organic compounds becomes a little confusing when the basics are misconstrued or not understood at all. I want to try my best to help you understand the basics of naming these compounds with some naming organic compounds worksheets.
It becomes even more confusing either when naming organic compounds with multiple methyls or naming organic compounds with functional groups or structures with strokes or dashes.
The first thing I would like to do is to lay down the IUPAC rules for naming organic compounds and then walk you through these basics with examples.
5 IUPAC rules for naming organic compounds
Rule 1: Take the longest continuous carbon chain
In naming organic compounds, there is a need to emphasize that the longest carbon chain could be branched and not necessarily straight.
As a matter of fact, there is no rule that states that the longest carbon chain must be straight.
Take a look at some examples.
Example 1
The longest carbon chain here for example is not the straight carbon chain but the branched carbon chain as a result it is a decane and not an octane
But how did I do deduce this, take a closer look here so you can understand how
So, taking the longest carbon chain from the branched-chain reveals that the organic compound is a decane.
And guys remember that I am yet to name the compound. The name of the compound is actually 4 methyl decane, don’t worry about the nomenclature we will get to see how the compound is named.
Another example is seen below
Rule 2: Identify the substituent groups attached to the chain
Ideally, the common substituents are the alkyl groups like methyl, ethyl, propyl etc
Also, the halo groups are commonly attached too and they are called choro group when chlorine is attached, the fluoro group when fluorine is attached and finally iodo group when iodine is attached.
Take a look at the example shown below.
You will see that there are four substituent groups in the structure above, actually, we have three methyl groups and one halo(fluoro) group.
How do I name this compound and which substituents should come first? I will show you in a jiffy how we can name this compound.
However, the name of the compound is 4 fluoro-2,2,6 trimethyl heptane, and hope you noticed the alphabetical trend in the nomenclature.
Let’s look at the second example on how to identify substituents.
Here too, we have four substituents two methyl groups, one ethyl group, and one chloro group.
Rule 3: Number the continuous carbon chain consecutively, starting at the end nearest a substituent group.
The numbering is quite important because we have situations where we get two or more nomenclatures from the same compound due to wrong numbering.
In fact, it is important I mention that only one numbering will be correct.
Rule 4: Designate the location of each substituent group by an appropriate number.
The next important rule is the ability to number the substituent groups attached to the largest carbon chain.
In doing this I would like to emphasize three guidelines that will help us in doing this.
Guideline 1
Start the numbering of the carbon chain and the substituent positioning from the substituent closest to the end of the chain.
Take a look at this example.
Wrong numbering
correct numbering
So, the correct numbering is the numbering that recognizes where the substituents stem from.
The rule of thumb is that you start the numbering from the end the substituent is closest to.
Guideline 2
There are situations that occur when you have substituents placed from the same positions when counting from both ends and then you don’t know where to start from.
Now listen when you have alkyl groups placed from same positions at both ends. Start from the bulky group.
Take a look at this
Where do I start numbering because the two alkyl groups viz methyl groups (CH3) and ethyl group (C2H5) are placed at the same positions from both ends?
The bulkier group should be considered in the numbering because that will yield the correct numbering.
So this is the correct numbering
Please do not be tempted to start from the methyl group numbering or always start from the right in numbering.
There is no rule that states that one should always start numbering from the right… No! There is no rule like that.
Guideline 3
When you have a halo group and an alkyl group on the same positions from both ends then you should start with the more inductive which is the halo group.
Take a look at this example.
It should be this way
Rule 5: Name the organic compound but take the naming of the substituents alphabetically.
There is a salient point I wish to make here and that is to name the substituents alphabetically.
Regardless of the positioning, for example, a chloro group should come before a fluoro group and an ethyl group should come before a methyl group in alphabetical trend.
Let’s then put these rules into practice and name these few compounds.
You can find 20 examples on naming organic compounds but here I will just give few examples.
Example 1
The numbering and name of this compound should be this
You can see I started from the ethyl substituents and now the nomenclature will be
3 ethyl -7 methyl nonane
Example 2
The correct numbering should as shown below
Then the naming of the compound is 3 chloro-7 methyl nonane
Generally naming of compounds requires practice and I am going to do a naming of organic compounds worksheet that will help you to practice and see the answers and your mistakes which will help you a great deal in your journey in chemistry.
I would love it if you will like me to do an e-book o naming organic compounds so I can know I should embark on it.
