Question

Number of isomers which can be obtained theoretically from monochlorination of 2 -methylbutane are (a) 2 (b) 3 (c) 4 (d) 5

Short answer

There are 3 distinct isomers for monochlorination of 2-methylbutane.

Step-by-step solution

Identify the carbon skeleton

2-Methylbutane has the chemical structure with a four-carbon chain and a methyl group on the second carbon. Its condensed structural formula can be written as: \( CH_3-CH(CH_3)-CH_2-CH_3 \).

Determine potential carbon centers for chlorination

Chlorination can occur at any hydrogen atom in the molecule. Analyze the structure of 2-Methylbutane: the carbons are denoted as C1, C2, C3, and C4, with C2 having the methyl group attached. Each carbon has a specific number of hydrogens that can be substituted: C1 and C4 have 3 hydrogens each, C2 has 1 hydrogen, and C3 has 2 hydrogens.

Identify unique substitution sites

The unique sites are where chlorination can produce different isomers. C1 and C4 provide the same substitution product due to symmetry; C2 is unique due to the methyl group, and C3 is also a unique site. Thus, while all carbon centers (C1/C4, C2, C3) can be chlorinated, C1 and C4 produce the same isomer.

Count the distinct monochlorinated isomers

Calculate the number of distinct chlorinated products: chlorination at C1 or C4 results in the same isomer, C2 creates a second distinct isomer, and C3 results in a third isomer. Hence, there are three distinct isomers possible from monochlorination of 2-Methylbutane.

Key concepts

Isomerism

Isomerism is a fascinating concept in organic chemistry. It involves molecules that have the same molecular formula but different structural configurations. This variance in structure can result in different chemical and physical properties. Let's understand this better:

• Structural Isomers: These isomers differ in the covalent arrangement of atoms. For example, both butane and isobutane have the formula \(C_4H_{10}\), but they differ in structure.
• Stereoisomers: In these isomers, the order of bonding is the same, but the spatial arrangement of atoms is different. Think of your hands; they are mirror images, but not superimposable.

When it comes to reactions like monochlorination, isomerism plays a crucial role. Since each carbon atom in a molecule like 2-Methylbutane can be chlorinated to form different compounds, understanding isomers helps us predict the possible outcomes.

Monochlorination

Monochlorination is a type of substitution reaction in organic chemistry. It involves replacing a hydrogen atom in an alkane with a chlorine atom, typically using chlorine gas in the presence of UV light. Here's how it works:

• Replacement: Only one hydrogen atom is replaced in monochlorination, leading to the formation of a haloalkane (alkyl halide).
• Reaction Conditions: This reaction often requires heat or light to initiate, as both help in breaking the \(Cl_2\) molecule into two reactive chlorine atoms.
• Selectivity: The selectivity of monochlorination is influenced by the type of carbon atom (primary, secondary, tertiary) where chlorination occurs, as different carbon atoms have varying reactivity levels with chlorine.

In the case of 2-Methylbutane, different carbon centers upon chlorination lead to the formation of distinct isomeric products.

2-Methylbutane

2-Methylbutane, also known as isopentane, is an interesting compound in organic chemistry known for its branched-chain structure. The unique arrangement of its atoms makes it a perfect candidate for studying reactions like chlorination.

Here's a closer look at its structure:

• Molecular Formula: The formula is \(C_5H_{12}\), and the structure branches due to a methyl group attached to the second carbon.
• Carbon Skeleton: The backbone is composed of four carbon atoms, with the second carbon bearing an additional methyl group, altering its chemical reactivity.
• Structural Representation: Its structural formula is written as: \(CH_3-CH(CH_3)-CH_2-CH_3\), highlighting the presence of three primary and one secondary carbon atoms.

Understanding 2-Methylbutane is crucial for determining possible chlorination sites and predicting the number of resulting isomers.

Reaction Mechanism

Understanding the reaction mechanism of chlorination helps demystify how isomers are formed. Once chlorination starts, here's how the process unfolds:

• Initiation: UV light or heat splits \(Cl_2\) into two chlorine radicals, kickstarting the reaction.
• Propagation: A chlorine radical abstracts a hydrogen atom from 2-Methylbutane, forming hydrochloric acid \((HCl)\) and an alkyl radical.
• Termination: The alkyl radical then combines with another chlorine radical to produce a monochlorinated product.

This multi-step process makes the chlorination of 2-Methylbutane possible, leading to different products based on which hydrogen atom gets replaced. Each unique replacement forms a distinct isomer, explaining the variation in reaction products.