Question

The IUPAC name of the compound \[C{H_2} = CH--CH{\left( {C{H_3}} \right)_2}\] is:
A. 1,1 - Dimethyl prop - 2 -ene
B. 3 - Methyl but - 1- ene
C. 2 - Vinyl propane
D. None of these

Answer 1

Hint: 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, considering the IUPAC name of the compound \[C{H_2} = CH--CH{\left( {C{H_3}} \right)_2}\] is:
Here the longest chain is with 4 carbons, so the word root is “but” it is from alkene so the suffix should be “ene”. There is a methyl group at the 3 position. Now the IUPAC name is, 3 – Methyl but - 1- ene.

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 to the name.