Question

Draw the condensed structural formula for the five isomers of hexane, \(\mathrm{C}_{6} \mathrm{H}_{14}\).

Short answer

The five isomers of hexane are n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane.

Step-by-step solution

Understand Isomer Concept

Isomers are compounds that have the same molecular formula but different structures. Hexane has the molecular formula \( \mathrm{C}_6 \mathrm{H}_{14} \), and we need to find all the structural variations of this formula.

Draw Linear Chain

Begin by drawing the linear chain or normal isomer of hexane, which is straight and consists of six carbon atoms connected sequentially. The condensed formula for straight-chain hexane is \( \mathrm{CH}_3(\mathrm{CH}_2)_4\mathrm{CH}_3 \).

Introduce Branching for First Isomer

Create the first branched isomer, where a single branch is attached to the second carbon in the chain. This is known as 2-methylpentane. The condensed formula is \( \mathrm{CH}_3\mathrm{CH}(\mathrm{CH}_3)\mathrm{CH}_2\mathrm{CH}_2\mathrm{CH}_3 \).

Introduce Different Branch Location

Create another isomer by moving the branch from the second to the third carbon. This is called 3-methylpentane. The condensed formula is \( \mathrm{CH}_3\mathrm{CH}_2\mathrm{CH}(\mathrm{CH}_3)\mathrm{CH}_2\mathrm{CH}_3 \).

Create Isomer with Two Branches

Create an isomer with two methyl branches. A common example is 2,2-dimethylbutane, with two methyl groups attached to the second carbon. The condensed formula is \( \mathrm{CH}_3\mathrm{C}(\mathrm{CH}_3)_2\mathrm{CH}_2\mathrm{CH}_3 \).

Another Isomer with Different Branching

Finally, create isomer with another branching arrangement, such as 2,3-dimethylbutane, with a methyl group on the second and third carbons. The condensed formula is \( \mathrm{CH}_3\mathrm{CH}(\mathrm{CH}_3)\mathrm{CH}(\mathrm{CH}_3)\mathrm{CH}_3 \).

Final review and Match Check

Verify these structures to confirm each has the formula \( \mathrm{C}_6 \mathrm{H}_{14} \). Ensure each structure presents a unique arrangement of the carbon atoms to confirm it is a true isomer.

Key concepts

Isomerism

Isomerism is a fascinating concept in organic chemistry, referring to compounds that share the same molecular formula but differ in how the atoms are arranged. This results in molecules having different properties despite being composed of the same number and types of atoms. A great example of isomerism can be seen in hexane, which has the molecular formula \( \mathrm{C}_6 \mathrm{H}_{14} \). There are several ways to arrange these 6 carbon and 14 hydrogen atoms, leading to different isomers known as structural isomers or constitutional isomers. These different structural configurations can lead to variations in physical properties like boiling points, melting points, and even chemical reactivity. It's a bit like having the same blocks to build a house, but arranging them in different patterns to create unique homes. Understanding isomerism is essential because it highlights the diversity possible within organic compounds and explains why some substances with identical formulas can behave so differently.

Structural Formulas

In organic chemistry, structural formulas are used to represent molecules, showing not just the number of atoms, but how they are connected. They provide a detailed picture of the molecule's structure and can vary from simple representations used for quick identification to more detailed configurations displaying each bond. For the molecular formula \( \mathrm{C}_6 \mathrm{H}_{14} \), knowing the structural formula helps to identify isomers. Each structural isomer features a different sequence or branching of carbon atoms. For example, linear hexane is shown as \( \mathrm{CH}_3(\mathrm{CH}_2)_4\mathrm{CH}_3 \). In contrast, a branched isomer such as 2-methylpentane is shown with a branching at the second carbon, represented as \( \mathrm{CH}_3\mathrm{CH}(\mathrm{CH}_3)\mathrm{CH}_2\mathrm{CH}_2\mathrm{CH}_3 \). These detailed formulas are pivotal in understanding how the position and relationships of atoms within a molecule influence the compound's chemical behavior and interactions. Thus, structural formulas serve as a fundamental tool for chemists to visualize and communicate the architecture of organic molecules.

Hydrocarbon Structures

Hydrocarbons are compounds composed solely of carbon and hydrogen atoms, and they form the backbone of organic chemistry. Hydrocarbon structures vary widely, from simple linear chains to more complex branched forms and even rings. In the case of hexane, \( \mathrm{C}_6 \mathrm{H}_{14} \), the linear form, sometimes called "n-hexane," consists of a straightforward chain of six carbon atoms. However, hydrocarbons often have branched structures, leading to various isomers. For example, 2-methylpentane and 3-methylpentane introduce methyl groups at different positions on the chain, while 2,2-dimethylbutane features two methyl branches on the second carbon. These small changes significantly affect the molecule’s properties. Hydrocarbons like hexane are foundational in many applications, from fuels to lubricants, due to their energy content and versatility. Understanding hydrocarbon structures is crucial for fields ranging from environmental science to industrial chemistry, as they form the building blocks of countless chemical reactions and products in our world.