Question

The number of chain isomers possible for hydrocarbon \(\mathrm{C}_{5} \mathrm{H}_{12}\) is (a) 3 (b) 5 (c) 4 (d) 6

Short answer

The number of chain isomers possible for \text{C}_5\text{H}_{12} is 3.

Step-by-step solution

Understand the Concept of Chain Isomers

Chain isomers are compounds with the same molecular formula but different arrangements of the carbon atoms. They differ in the branching of the carbon chain.

Draw the Possible Isomers for \text{C}_5\text{H}_{12}

Begin by drawing the straight-chain isomer with five carbon atoms all in a row. Then draw all other combinations with less than five carbons in the main chain and different branching patterns, ensuring to not duplicate any that are simply rotations or reflections of one another.

Count the Isomers

After drawing all the distinct structures, count the number of valid unique isomers to find the total number of chain isomers possible.

Key concepts

IUPAC Nomenclature

Understanding the International Union of Pure and Applied Chemistry (IUPAC) nomenclature is essential for identifying and naming organic compounds systematically. The nomenclature process begins with identifying the longest chain of carbon atoms in the hydrocarbon, which serves as the parent chain. The parent chain is then numbered to give the lowest possible numbers to the substituents attached to it.

For branched hydrocarbons, like chain isomers, the substituents (branches) are named by removing the suffix '-ane' from the corresponding alkane and adding '-yl'. For example, a one-carbon branch is called a methyl group. The position of the substituent on the parent chain is indicated by a number corresponding to the carbon it's attached to. When there are multiple identical substituents, prefixes such as 'di-', 'tri-', 'tetra-', etc., are used to indicate their quantity.

Let's apply IUPAC naming rules to the isomers of \text{C}\(_5\)\text{H}\(_{12}\). The straight-chain isomer, with all carbons in a row, is named pentane. When the chain is four carbons long with a one-carbon branch, the compound is named 2-methylbutane, indicating a methyl group on the second carbon of butane. A further possibility is two methyl groups on the third carbon of propane, named 2,2-dimethylpropane.

IUPAC nomenclature ensures each organic compound has a unique, universally understood name, aiding effective communication among scientists and students.

Structural Isomerism

Structural isomerism, also known as constitutional isomerism, refers to the phenomenon where compounds have the same molecular formula but different structural formulas. In the context of hydrocarbons, this includes varying carbon chain lengths and branching patterns as seen in chain isomers.

These isomers have different physical and chemical properties despite having the same number of each atom. For instance, their boiling points, melting points, and densities can differ significantly. The reason for these differences lies in the varied shape and structure which influences intermolecular forces. For example, straight-chain hydrocarbons generally have higher boiling points compared to their branched counterparts due to the larger surface area available for van der Waals interactions.

Isomerism is a critical concept in chemistry because it demonstrates how molecular structure impacts the properties of a substance. Understanding isomers expands the potential variation and complexity of organic compounds, influencing everything from pharmaceutical design to the development of new materials.

Organic Compound Structural Representation

Structural representation in organic chemistry is a crucial skill that aids in visualizing and understanding the complex arrangements of atoms within a molecule. The most common forms of representation include Lewis structures, structural formulas, and skeletal formulas.

Lewis structures show all atoms, bonds, and lone pairs of electrons, providing detailed insight into a molecule's electronic arrangement. Structural formulas are slightly simplified, presenting the molecule in a two-dimensional form where lines represent chemical bonds and letters represent elements. The most simplified, the skeletal formula, shows the carbon skeleton of organic molecules, where vertices and line ends represent carbon atoms, and hydrogen atoms are typically omitted unless they are attached to functional groups.

For example, the skeletal formula of pentane is a straight line with four vertices, while the skeletal formula of 2-methylbutane branches at the second vertex. These structural representations not only help in understanding and predicting the physical and chemical properties of compounds but also in communicating complex molecular information efficiently.