Question

The number structural isomers for pentene are:
A. 3
B. 4
C. 5
D. 6

Answer 1

Hint- In order to find the number of structural isomers for pentene first we have to understand the term isomers and pentene. Then we will look for all the combinations possible.

Complete answer:
Let us understand the given structure that is pentene
Pentene is a compound with five carbon atoms and a double bond. If we break apart the name of the compound, then the structure makes sense. The 'pent-' part means 'five' and refers to the longest chain of five carbon atoms. The “ene” part refers to a double bond somewhere in the molecule. The chemical formula for pentene is: \[{C_5}{H_{10}}\] . The most basic five carbon chain will have a chemical formula of: \[{C_5}{H_{12}}\] , but as pentene has a double bond, it has two less hydrogen atoms.
Now we will discuss about isomers,
So, an isomer is when a compound has the same chemical structure but the atoms are arranged differently.
There are five isomers of pentene: 1-pentene, 2-pentene, 2-methyl but-1-ene, 3-methyl but-1-ene, 2-methyl but-2-ene.
Pentene isomers contain one double bond between the two carbon apart from 5 carbon and 10 hydrogen atoms.
Hence, there are 5 structural isomers of pentene as mentioned above.

Hence the correct answer is option C.

Note- Apart from these 5 structural isomers there are also two stereo isomers of pentene possible, which are represented by “cis” and “trans” form. “Cis” means same or, on this side in Latin, meaning that in cis-2-pentene, the functional groups in the molecule are on the same side, making it a “cis” conformation. “Trans” means across or on the fair side in Latin, meaning that in trans -2- pentene, the functional groups in the molecular are on opposite sides, making it a “trans'' conformation.