Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of possible enantiomeric pairs that can be produced during monochlorination of 2 -methyl butane are (a) 2 (b) 3 (c) 4 (d) 1

Step-by-Step Solution

Answer

The number of enantiomeric pairs is 2.

Step 1: Understanding the Problem

Monochlorination of 2-methylbutane involves replacing one hydrogen atom with a chlorine atom. The problem asks to find how many enantiomeric pairs result from this chemical reaction.

Step 2: Identifying Chiral Centers

In 2-methylbutane, a chiral center is a carbon atom with four different substituents. Look at the carbon atoms in the structure of 2-methylbutane to identify potential chiral centers after chlorination.

Step 3: Exploring Chlorination Sites

In 2-methylbutane, there are five potential sites for chlorination - each hydrogen atom attached to different carbon atoms (C2, C3, and C4 as distinct due to symmetry). Identify which sites would lead to the formation of a chiral center.

Step 4: Forming Chiral Centers

Upon substitution of a hydrogen atom with chlorine on C2, C3, and C4, we must determine which sites create a new chiral center. Only the substitution at C2 and C3 leads to chiral centers, as they generate carbon atoms with four different substituents.

Step 5: Counting Enantiomeric Pairs

Each chiral center leads to the formation of enantiomers. Since only substitutions at C2 and C3 both have been identified to lead to chiral centers, count how many enantiomeric pairs are viable. C2 and C3 each form one pair of enantiomers each.

Step 6: Concluding the Result

Since substitution product at C2 and C3 results in two pairs of enantiomers in total, the final answer is determined based on enantiomeric pair formation.

Key Concepts

Enantiomers

Enantiomers are a fascinating concept in chemistry that can significantly affect the properties of a molecule. These are two molecules that are non-superimposable mirror images of each other, much like our left and right hands. Enantiomers occur when a molecule has a chiral center, which means it is asymmetric. This asymmetry allows the molecule to exist in two different forms that are mirror images. Why are enantiomers important? They have identical physical properties, such as melting and boiling points, but they often interact very differently with other chiral substances, including biological molecules. Here's what to remember about enantiomers:

• They are mirror images that cannot be perfectly aligned.
• Enantiomers have identical physical properties but can have different chemical behaviors, especially in biological systems.

Understanding the concept of enantiomers helps in predicting how a molecule will interact in different environments and with different compounds.

Chiral Centers

A chiral center is at the heart of an enantiomer and is crucial in determining the molecule's properties. In simple terms, a chiral center is a carbon atom bonded to four different substituents or groups. This uniqueness at the chiral center leads to the asymmetry that allows molecules to exist as enantiomers. When a molecule undergoes a reaction, like monochlorination, identifying potential chiral centers helps predict if and how new enantiomers can form. For example, in 2-methylbutane:

• A chiral center occurs when the substitution creates four different groups attached to a carbon.
• In monochlorination, the chlorine atom replaces a hydrogen on the carbon atom, potentially leading to new chiral centers.

Chiral centers are fundamental in studying reactions and understanding the formation of different stereoisomers, aidind chemists to plan and rationalize chemical synthesis.

2-Methylbutane

2-Methylbutane is an organic compound with a branched alkane structure. It is composed of five carbon atoms and twelve hydrogen atoms (C₅H₁₂), and it is known for its straightforward yet structurally intricate formation. Let's break down the significance of 2-methylbutane in spectacular detail:

• In the name '2-methylbutane', 'butane' indicates a four-carbon chain, and '2-methyl' means a methyl group (CH₃) is attached to the second carbon of this chain.
• During monochlorination, replacing a hydrogen atom with a chlorine at specific sites can yield different structural forms, affecting symmetry and potentially creating chiral centers.

Understanding the structure and behavior of 2-methylbutane when it reacts is vital for predicting the kind of enantiomeric pairs that can form. This knowledge is critical for anyone studying organic chemistry, especially when looking at reactions involving hydrocarbons.