Question

IUPAC name of the compound $C{{H}_{3}}-CH=CH-C{{H}_{3}}$is:
(A) 2-butene
(B) 1-butene
(C) 3-pentene
(D) 2-pentene

Answer 1

Hint: Try solving this question selecting the main chain, numbering it and choosing the root word. Then check it for being an alkane, alkene or alkyne. A compound having single, double, triple bond is known as alkane, alkene, alkyne, respectively.

Complete step by step answer:
Let us start naming the organic compound according to the rules of IUPAC nomenclature

We must start by selecting the longest carbon chain, which, as we can see in the question, is composed of four carbons. So, the root word is ‘but’.Now let us check the organic compound if it has a double or triple bond.
As we can see that the second carbon from the left has a double bond. So, the compound is an alkene. Therefore, its name becomes ‘butene’.
Now let us number the organic compound. We can number it from either left or right because either way, the double bond will be at the second carbon. Therefore, the name finally becomes – but-2-ene or 2-butene.
Therefore, the answer is – option (a) – IUPAC name of the compound $C{{H}_{3}}-CH=CH-C{{H}_{3}}$ is 2-butene.

Additional Information:
Alkanes are known as saturated hydrocarbons, whereas alkenes and alkynes are known as unsaturated hydrocarbons.

Note: The table for root words of organic compound according to the number of carbons is as follows–

Number of Carbons	Root word
1	Meth
2	Eth
3	Prop
4	But
5	Pent
6	Hex
7	Hept
8	Oct