Question

The possible number of alkyl group of molecular formula \(\mathrm{C}_{5} \mathrm{H}_{11}\) is (A) 5 (B) 6 (C) 7

Short answer

There are 5 possible alkyl groups of the molecular formula C5H11, which are derived from the structural isomers of C5H12: n-pentane, isopentane (methylbutane), and neopentane (dimethylpropane). These 5 alkyl groups are n-pentyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, and 1,1-dimethylpropyl. Therefore, the correct answer is \( \boxed{(A) \thinspace 5} \).

Step-by-step solution

Identify different structural isomers of C5H12.

First, we need to find all the structural isomers of C5H12. Structural isomers are compounds with the same molecular formula but different structural arrangements of the atoms. There are three structural isomers of C5H12: n-pentane, isopentane (methylbutane), and neopentane (dimethylpropane). Their structural formulas are as follows: 1. n-pentane: -CH3CH2CH2CH2CH3 2. isopentane (methylbutane): (-CH3)2CHCH2CH3 3. neopentane (dimethylpropane): (-CH3)3CCH3

Convert C5H12 isomers into alkyl groups of C5H11.

Now, we can convert these three structural isomers of C5H12 into alkyl groups of C5H11 by removing one hydrogen atom from each isomer. 1. By removing a hydrogen atom from n-pentane, we get n-pentyl: -CH2CH2CH2CH2CH3 2. By removing a hydrogen atom from isopentane (methylbutane), we can get two different alkyl groups: - 2-methylbutyl: -CH(CH3)CH2CH2CH3 - 3-methylbutyl: -CH2CH(CH3)CH2CH3 3. By removing a hydrogen atom from neopentane (dimethylpropane), we can get two different alkyl groups: - 2,2-dimethylpropyl: -CH(C(CH3)3)CH2 - 1,1-dimethylpropyl: -C(CH3)2CH2CH3

Count all possible alkyl groups of C5H11.

Upon following the above steps, we found out that there are 5 possible alkyl groups with a molecular formula of C5H11: 1. n-pentyl 2. 2-methylbutyl 3. 3-methylbutyl 4. 2,2-dimethylpropyl 5. 1,1-dimethylpropyl Therefore, the correct answer is (A) 5.

Key concepts

Structural Isomers

Understanding structural isomers is crucial to grasping organic chemistry concepts. Structural isomers, as the name implies, have the same molecular formula but differ in the arrangement of the atoms within the molecule. This difference in structure can affect the physical and chemical properties of the compounds despite having the same numbers of each type of atom.

For example, in the solution to the given problem, the molecular formula \(\mathrm{C}_{5}\mathrm{H}_{12}\) represents a family of molecules known as pentanes. Here, there are three structural isomers: n-pentane, isopentane (also known as methylbutane), and neopentane (dimethylpropane). The isomers differ in how the carbon atoms are connected, leading to various chain and branch structures in the molecule.

Recognizing this fundamental concept in organic chemistry helps learners understand how complexity can arise from simple formulas and lays the foundation for predicting the properties and reactivities of organic compounds.

Organic Chemistry

Organic chemistry focuses on the study of carbon-containing compounds, which encompasses a vast array of substances including pharmaceuticals, plastics, and DNA. The essence of organic chemistry lies in the understanding of molecular structures, bonds, and reactions of organic molecules.

The rules of organic chemistry dictate how atoms can be linked, leading to the vast diversity of organic compounds. The concept of alkyl groups, featured in the textbook exercise, showcases how a single formula can give rise to multiple groups based on the connection of carbon and hydrogen atoms. Alkyl groups are essentially hydrocarbon chains that are missing one hydrogen atom, which makes them reactive entities capable of binding to various other atoms or molecular groups.

To compliment learning from textbook exercises, it's helpful to visualize molecules using structural drawings or molecular models. This enhances spatial understanding of molecular geometry, making it easier to distinguish between different organic structures, such as the alkyl groups derived from the various isomers of pentane.

JEE Main and Advanced Preparation

Preparing for competitive exams like the JEE Main and Advanced requires diligent study and a thorough understanding of concepts such as isomerism in organic chemistry. Critical thinking and problem-solving are vital skills for these exams; the ability to analyze a problem, as in the given exercise, and apply conceptual knowledge to find a solution is key.

For effective preparation, students should focus on mastering fundamental concepts, practicing a variety of problems, and understanding the logic behind each step of a solution. Strategies may include creating a well-structured study plan, engaging in consistent practice, and reviewing solutions to understand common pitfalls and how to avoid them.

In addition to textbooks, aspirants can benefit from online educational platforms that offer a variety of practice questions and step-by-step solutions to enhance their studies. Mock tests aligned with the exam pattern also provide valuable experience in managing time and applying concepts under exam conditions. Always remember to analyze your practice test results to identify areas that require more focus for a well-rounded preparation strategy.