Problem 8 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The number of isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\) is (a) 4 (b) 5 (c) 6 (d) 7

Step-by-Step Solution

Answer

There are 5 isomers of \( \mathrm{C}_{6} \mathrm{H}_{14} \).

Step 1: Understanding Isomers

Isomers are molecules that have the same molecular formula but different structural arrangements. For alkanes like \( \mathrm{C}_{6} \mathrm{H}_{14} \), which is hexane, the structural isomers differ by the arrangement of carbon atoms.

Step 2: Identify the Basic Structural Isomer

Start with the simplest structure: a straight-chain hexane. This is called n-hexane. This structure involves a continuous chain of six carbon atoms.

Step 3: Form Branched Isomers

Create isomers by branching the carbon chain. - Remove one carbon from the end and attach it to the second or third carbon to form 2-methylpentane and 3-methylpentane. - Create more branching: move two of the end carbons to form 2,3-dimethylbutane and another isomer. Continue until no more unique structures can be formed.

Step 4: Enumerating all Possible Isomers

Now that all possible unique arrangements are understood, count them: 1. n-Hexane2. 2-Methylpentane3. 3-Methylpentane4. 2,2-Dimethylbutane5. 2,3-DimethylbutaneThus, there are five structural isomers for \( \mathrm{C}_{6} \mathrm{H}_{14} \).

Key Concepts

Molecular Formula

The molecular formula of a compound is a concise way to express the number and types of atoms that make up that molecule. For example, the molecular formula \( \mathrm{C}_{6} \mathrm{H}_{14} \) indicates that this compound consists of 6 carbon atoms and 14 hydrogen atoms. This formula does not tell us how these atoms are arranged or linked, only their quantities.
When discussing isomers, the molecular formula remains the same, even though the arrangement can vary significantly.
This is important in understanding that many different compounds can share the same molecular formula if their atoms are configured differently.

Structural Isomers

Structural isomers are compounds that have the same molecular formula but differ in the connectivity of the atoms within the molecules. This means that although the number of each type of atom is the same in each isomer, the way they are arranged can create entirely distinct substances.
This is often highlighted in organic chemistry with alkanes, where the carbon skeleton can be rearranged to form different shapes.

• In linear isomers, the carbon atoms are arranged in a single line.
• In branched isomers, one or more carbon atoms are bonded to multiple carbons, forming branches off the main chain.

It's fascinating to note how changing the arrangement can completely alter the properties and characteristics of the molecule.

Alkanes

Alkanes are a fundamental group in organic chemistry. They are hydrocarbons, which means they are composed exclusively of hydrogen and carbon atoms. More specifically, alkanes are saturated hydrocarbons, meaning they only contain single covalent bonds between carbon atoms.
The general formula for alkanes is \( C_nH_{2n+2} \), where \( n \) represents the number of carbon atoms. This formula helps determine the number of hydrogen atoms present
. Alkanes like hexane are often quite stable and are found in various fuels and substances in everyday life.

• They are non-polar due to their symmetrical structure.
• Despite their simplicity, they can take on complex isomeric forms.

Alkanes form a perfect example of how simple components can lead to diverse and highly functional molecules.

Hexane

Hexane is a specific alkane with the molecular formula \( \mathrm{C}_{6} \mathrm{H}_{14} \). As an alkane, it consists solely of carbon and hydrogen atoms connected by single bonds.
Let's explore the characteristics of hexane in more detail:

• It is typically found as a clear liquid with a faint petroleum-like odor.
• Hexane is often used industrially, especially as a solvent in the extraction of vegetable oils from seeds.

The structural isomerism of hexane is particularly interesting because it illustrates how different configurations of the same atoms can lead to different substances. Hexane itself can be arranged to form five different isomers, each with unique properties and uses, reinforcing the diverse applications and chemical dynamics of this simple molecule.