Question

What is the IUPAC name of the following alkene?
$C{H_2} = CH - CH{\left( {C{H_3}} \right)_2}$
A.Isopropyl ethylene
B.$2$-methyl but-$3$-ene
C.Isopentene
D.$3$-methyl but-$1$-ene

Answer 1

Alkenes are unsaturated hydrocarbons consisting of only carbon and hydrogen atoms. There is a presence of double bond in alkenes. The substituents and double bonds present in alkenes will get numbering. The lowest numbering must be considered and the longest chain must be considered while naming alkenes.

Complete answer:
Hydrocarbons are the compounds consisting of only carbon and hydrogen atoms. Alkenes are unsaturated compounds consisting of carbon and hydrogen atoms. In addition to these atoms, there is a presence of a double bond. The general molecular formula of alkenes is ${C_n}{H_{2n}}$, where n is the number of carbon atoms.
The longest carbon chain must be considered while writing the IUPAC name of alkenes. Given compound consists of five carbon atoms. The base chain has four carbon atoms. Thus, the root word will be but.
There is a methyl substituent and double bond. The methyl substituent gets the number $3$ and the double bond position will be $1$.
Thus, the name of the given alkene is $3$-methyl but-$1$-ene.

Option D is the correct one.

Note:
IUPAC nomenclature some rules must be considered and has to write the name according to it. If the numbering starts from the right side the double bond and substituents numbering will be five. But, if numbering starts from the left side, the double bond gets $1$ and the methyl substituent gets $3$. The sum of the both numbers will be equal to $4$.