Question

How many isomers of butane are possible ?

• A. 2
• B. 3
• C. 4
• D. 5

Hint:

To find isomers, always start by drawing the longest possible straight chain. Then, shorten the main chain by one carbon and try to place it as a branch at different valid positions.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Isomers are molecules that have the same molecular formula but a different arrangement of atoms in space. The question asks for the number of structural isomers for butane (\(C_4H_{10}\)).

Step 2: Detailed Explanation:
The molecular formula for butane is \(C_4H_{10}\). We can arrange the four carbon atoms in two different ways to form a stable structure:
\begin{enumerate} \item A straight chain: The carbon atoms are linked one after another in a continuous chain. This isomer is called n-butane.
\[ CH_3 - CH_2 - CH_2 - CH_3 \] \item A branched chain: Three carbon atoms form a chain, and the fourth carbon atom is attached as a branch to the central carbon atom. This isomer is called isobutane (IUPAC name: 2-methylpropane).
\[ \begin{array}{c} CH_3
|
CH_3 - CH - CH_3 \end{array} \] \end{enumerate} There are no other ways to connect four carbon atoms and ten hydrogen atoms to form a different structure.

Step 3: Final Answer:
There are two possible structural isomers for butane: n-butane and isobutane.