Problem 2 - General Chemistry

Question

Draw structural formulas of the five isomers of \(\mathrm{C}_{6} \mathrm{H}_{14}\)

Step-by-Step Solution

Answer

The five isomers of \( \text{C}_6\text{H}_{14} \) are hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane.

Step 1: Understand the Problem

We need to draw the structural formulas for the five isomers of the molecular formula \( \text{C}_6\text{H}_{14} \). Here, an isomer refers to a compound with the same molecular formula but a different structural arrangement of atoms.

Step 2: Draw the First Isomer - Hexane

The simplest isomer is n-hexane, where six carbon atoms are connected in a straight chain: \( \text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_3 \).

Step 3: Draw the Second Isomer - 2-Methylpentane

To form 2-methylpentane, place a methyl group \( (\text{CH}_3-) \) on the second carbon of a five-carbon chain: \( \text{CH}_3\text{-CH(CH}_3\text{)-CH}_2\text{-CH}_2\text{-CH}_3 \).

Step 4: Draw the Third Isomer - 3-Methylpentane

For 3-methylpentane, place a methyl group on the third carbon of a five-carbon chain: \( \text{CH}_3\text{-CH}_2\text{-CH(CH}_3\text{)-CH}_2\text{-CH}_3 \).

Step 5: Draw the Fourth Isomer - 2,2-Dimethylbutane

In 2,2-dimethylbutane, add two methyl groups to the second carbon of a four-carbon chain: \( \text{CH}_3\text{-C(CH}_3\text{)_2\text{-CH}_2\text{-CH}_3} \).

Step 6: Draw the Fifth Isomer - 2,3-Dimethylbutane

Place one methyl group each on the second and third carbon of a four-carbon chain: \( \text{CH}_3\text{-CH(CH}_3\text{)-CH(CH}_3\text{)-CH}_3 \).

Key Concepts

structural formulas

Chemical compounds can have the same molecular formula but differ in how their atoms are arranged or connected. These differences in arrangement are shown through structural formulas. Such formulas are visual representations that depict the bonding relationships between atoms in a molecule. They are crucial because they provide insight into the shape and function of a compound.

When drawing structural formulas, it's important to:

• Identify the total number of atoms.
• Understand how many bonds each atom can make.
• Arrange the atoms to reflect the specific structure of an isomer.

This becomes apparent when considering isomers, which are compounds with identical molecular formulas but different structures. Each unique arrangement gives the compound distinct properties.

n-hexane

One of the simplest ways to arrange the \(\text{C}_6\text{H}_{14}\) molecule is in a straight chain, known as n-hexane. This isomer features a continuous chain of six carbon atoms connected linearly, with hydrogen atoms filling all remaining valences. The formula for n-hexane can be written as \(\text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_3\).

N-hexane is known for being the most straightforward chain isomer of hexane. Its linear structure influences its properties, such as having a relatively higher boiling point compared to its more branched counterparts. Straight-chain alkanes like n-hexane are key in understanding basic concepts of organic chemistry.

methyl group

A methyl group, typically represented as \(\text{CH}_3-\), is a fundamental component in organic chemistry. It consists of one carbon atom bonded to three hydrogen atoms. Adding a methyl group to a hydrocarbon chain can significantly alter the compound's properties and structure, creating different isomers.

In the context of \(\text{C}_6\text{H}_{14}\) isomers, methyl groups are used to create branching within the carbon chain. For example, when designing 2-methylpentane, the methyl group is attached to the second carbon in the five-carbon chain, resulting in a different structural arrangement than straight-chain hexane. This demonstrates how methyl groups can drastically change the arrangement and properties of a molecule.

dimethylbutane

1,1-Dimethylbutane is a common way to demonstrate branching in \(\text{C}_6\text{H}_{14}\) isomers. It involves adding two methyl groups, typically on the same or adjacent carbon atoms, to a base hydrocarbon chain.

In the case of 2,2-dimethylbutane, two methyl groups are added onto the second carbon of a four-carbon chain, forming a compound represented by the formula \(\text{CH}_3\text{-C(CH}_3\text{)_2\text{-CH}_2\text{-CH}_3}\). This structural addition significantly influences the boiling point and physical shape of the molecule. Similarly, 2,3-dimethylbutane involves placing a methyl group on both the second and third carbon atom, creating a distinctively branched isomer. These forms showcase the diversity in molecular structures and are crucial for understanding the breadth of organic chemistry.