Question

What is chain isomerism? How many structural isomers are possible for the compound with molecular formula \(\mathrm{C}_{4} \mathrm{H}_{10} ?\)

Short answer

Answer: Chain isomerism is a type of structural isomerism in which carbon atoms in a hydrocarbon molecule are connected differently, leading to various arrangements of the same molecular formula. For the molecular formula \(\mathrm{C}_{4} \mathrm{H}_{10}\), there are two possible chain isomers: butane and isobutane.

Step-by-step solution

Defining Chain Isomerism

Chain isomerism is a type of structural isomerism in which the carbon atoms in a hydrocarbon molecule are connected differently, leading to various arrangements of the same molecular formula. These chain isomers have the same number of atoms and the same number of bonds but differ in their structural arrangement.

Molecular Formula

The given molecular formula is \(\mathrm{C}_{4} \mathrm{H}_{10}\). This formula represents an alkane with 4 carbon atoms and 10 hydrogen atoms.

Drawing Possible Structural Isomers

To find the number of possible structural isomers, we can draw different structural formulas while following the rules of chain isomerism. We should consider all rearrangements of the carbon atoms and their attached hydrogen atoms, ensuring that the total number of carbon and hydrogen atoms remains the same.

Counting Structural Isomers

For the given molecular formula \(\mathrm{C}_{4} \mathrm{H}_{10}\), there are two possible structural isomers: 1. Butane (n-butane): \(\chemfig{-[:0]-[:-60]-[:0]-[:-60]}\) 2. Isobutane (methylpropane): \(\chemfig{(-[:0]) -[:-60](-[:295])-[:0]}\) These two structural isomers have the same molecular formula but differ in the arrangement of carbon atoms, making them chain isomers.

Key concepts

Understanding Structural Isomers

Structural isomers are molecules with the same molecular formula but different structural arrangements of atoms. This property causes them to have distinct physical and chemical properties.
Structural isomerism is further classified into several types, one of which is chain isomerism. Chain isomerism occurs when the carbon skeleton of the compounds is arranged differently, leading to various linear and branched forms.

For example, in alkanes, which are hydrocarbons with single bonds between carbon atoms, chain isomerism can be easily demonstrated. Alkanes with four or more carbon atoms can form chain isomers, such as n-butane and isobutane.

To identify these isomers, it's essential to look at how the carbon atoms are connected. Despite having the same molecular formula, the different connections alter how these compounds react with other substances and how they behave under different conditions.

The Significance of Molecular Formula

The molecular formula provides crucial information about a compound, specifying the types and numbers of atoms present. In organic chemistry, the molecular formula is particularly valuable as it can indicate the possibility of structural isomerism.

For instance, the molecular formula \( \mathrm{C}_{4} \mathrm{H}_{10} \) indicates an alkane with four carbon atoms and ten hydrogen atoms, but it does not tell us about the structure of the molecule. That's where isomerism comes into play. Given this formula, we can infer that there may be multiple ways to arrange these atoms—creating structural isomers.

With a clear understanding of the molecular formula, students and chemists can predict and draw different isomers' structures. This ability is essential for comprehending the diverse behavior of organic molecules in chemical reactions and their applications in various fields of science and industry.

Alkanes and Their Isomers

Alkanes are the simplest type of organic compounds, consisting only of carbon and hydrogen atoms with all single bonds, following the general formula \( C_nH_{2n+2} \). With enough carbon atoms, alkanes can exhibit chain isomerism, leading to the existence of multiple distinct structures for the same molecular formula.

As the number of carbon atoms in an alkane increases, the structural complexity and the potential for isomerism grow exponentially. For instance, while propane, with three carbon atoms, does not have chain isomers, butane, with four carbon atoms, has two chain isomers, which are n-butane and isobutane.

Understanding alkanes and their structural isomers is fundamental for students to grasp the variety and versatility of organic molecules. It also lays the groundwork for learning about more complex hydrocarbons and the sophisticated structures they can form—each with unique characteristics and uses.