Question
Question: The IUPAC name of 
(A) 2 -Methylcyclohexane
(B) 1 -Methyl-2-cyclohexene
(C) 6 -Methylcyclohexane
(D) 3 - Methylcyclohexene
Solution
To name this structure you should know the IUPAC nomenclature. IUPAC names are combined with the primary prefix, root word, and primary suffix. By this, each compound can be named unique. Primary prefixes are used to indicate the origin of the compound in IUPAC nomenclature. Prefixes are used to differentiate the cyclic and acyclic molecules in IUPAC nomenclature.
Complete step by step answer:
In the IUPAC nomenclature case, the root word is the number of total carbons in the longest chain of that compound.
| No. of carbons | Root word |
|---|---|
| 1 | Meth |
| 2 | Eth |
| 3 | Prop |
| 4 | But |
| 5 | Pent |
… and so on.
The primary suffix is used to differentiate between the saturated compounds (Alkanes) and unsaturated compounds (Alkene and Alkynes).
| compound | Suffix |
|---|---|
| Alkane | Ane |
| Alkene | Ene |
| Alkyne | Yne |
If there is more than one suffix. Then one of those suffixes is considered as the secondary suffix.
Example: Methanol (Alkanol), here ‘ol’ is a secondary suffix.
The primary prefixes are used to differentiate between cyclic compounds and noncyclic or chain compounds. For cyclic compound prefix s ‘cyclo’. if there are any side chains or groups are present then secondary prefixes like ‘methyl’, ‘ethyl’, ‘propyl’, ‘isopropyl’ are used.
Now the given compound is,
The name of this compound is 1 -Methyl-2-cyclohexene.
It is a cyclic compound so the “cyclo” prefix is used. Six carbon is present in the ring so “hex” is the word root. And it has a double bond so, “ene” is used as a primary suffix. In this compound as there is a methyl group present so, “1-methyl” is for the alkyl group.
So, the correct option is B.
Note: For example, the structure of lindane is,
The IUPAC name of lindane is gamma-hexachlorocyclohexane. It is also called benzene hexachloride.
In this structure two chlorine atom which is cis to each other are at gamma position, that is why gamma is written in the IUPAC name.
It is a cyclic compound so the “cyclo” prefix is used. Six carbon is present in the ring so “hex” is the word root. And “ane” is used as a primary suffix.
There are six chlorine atoms are present that is why “hexa cholo” is added in the name.