Nomenclature of Compounds Containing Complex Substituents

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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

  1. 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.
  2. On the complex substituent, numbering is done from the end attached to the principal chain.

Example

IUPAC Nomenclature of Saturated Hydrocarbons, Carbon Types example : 5-(2-Ethylbutyl)-2,3-dimethyldecane

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

IUPAC Nomenclature of Saturated Hydrocarbons, Carbon Types example : 5-(2-Ethylbutyl)-2,3-dimethyldecane

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. 1-Methylpropyl
  2. 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.

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