Nomenclature of Compounds Containing Complex Substituents
You should be able to name the compound given below (if not, read our previous tutorials).
4-Ethylheptane
Now, how will you name this compound :
In the above example, the branched chain contains a branch. These type of branched chain substituents are known as complex substituents.
Rules for naming complex substituents
Numbering is done separately on complex substituents and number 1 is assigned to the carbon attached to the parent chain.
4-(1-Methylethyl)heptane
Note : The name of complex substituent is enclosed in brackets to avoid any confusion.
When two chains of equal size are present
- The chain with more number of side chains forms a part of the longest carbon chain while the other one is considered the complex
substituent.
- On the complex substituent, numbering is done from the end attached to the principal chain.
Example
5-(2-Ethylbutyl)-2,3-dimethyldecane
Alphabetical order in complex substituents
Prefixes like di, tri, tetra etc. are considered while deciding the
alphabetical order of complex substituent.
Recall : Prefixes like di, tri, tetra are not considered
while deciding the name of an alkyl group.
Example
5-(1,1-Dimethylpropyl)-4-ethylnonane
First point of difference in complex substituents
The following example should be able to teach you the concept, provided you have understood everything we have taught so far.
The above compound contains two complex substituents :
- 1-Methylpropyl
- 2-Methylpropyl
Clearly, both the substituents are methylpropyl. Only the location of methyl is different.
In such situations, where the names of two or more substituents are composed of identical words, the one having the lowest locant
at first cited point of difference within the complex substituent is written first.
Hence, the name of the above formula will be 5-(1-methylpropyl)-6-(2-methylpropyl)decane.
More than one Occurrence of Complex Substituents
Prefixes bis (for two), tris (for three), tetrakis (for four) etc. are used (not di, tri, tetra etc. ) when the
same complex substituent appears more than once in a compound.
4,6-Bis(1,1-dimethylethyl)nonane
Do not confuse
Prefixes di, tri, tetra etc. are not considered while naming an alkyl group but are considered while
naming a complex substituent.
2,2,7-Trimethyl-4-(1-methylpropyl)nonane
Tri is not considered while naming alphabetically because methyl is an alkyl group not a complex substituent. Since methyl comes before
methylpropyl (as in any dictionary), it is written first.