Problem 25 - Chemistry Matter and Change

Question

Draw all of the structural isomers possible for the alkane with the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{14}\) . Show only the carbon chains.

Step-by-Step Solution

Answer

The five structural isomers of C6H14 are: 1. Hexane (linear): \[CH_{3} - CH_{2} - CH_{2} - CH_{2} - CH_{2} - CH_{3}\] 2. 2-Methylpentane: \[CH_{3} - CH(CH_{3}) - CH_{2} - CH_{2} - CH_{3}\] 3. 3-Methylpentane: \[CH_{3} - CH_{2} - CH(CH_{3}) - CH_{2} - CH_{3}\] 4. 2,2-Dimethylbutane: \[CH_{3} - CH(CH_{3})CH(CH_{3}) - CH_{3}\] 5. 2,3-Dimethylbutane: \[CH_{3} - CH(CH_{3}) - CH(CH_{3}) - CH_{3}\]

Step 1: 1. Hexane (linear)

The carbon skeleton of hexane is a straight chain of six carbon atoms connected by single bonds: \[CH_{3} - CH_{2} - CH_{2} - CH_{2} - CH_{2} - CH_{3}\] Now, let's move on to the branched isomers.

Step 2: 2. 2-Methylpentane

This isomer has five carbon atoms in the longest chain and one carbon atom branching off from the second carbon atom in the chain: \[CH_{3} - CH(CH_{3}) - CH_{2} - CH_{2} - CH_{3}\]

Step 3: 3. 3-Methylpentane

This isomer also has five carbon atoms in the longest chain, but the branching occurs at the third carbon atom instead: \[CH_{3} - CH_{2} - CH(CH_{3}) - CH_{2} - CH_{3}\]

Step 4: 4. 2,2-Dimethylbutane

This isomer has four carbon atoms in the longest chain, with two methyl groups branching off from the second carbon atom: \[CH_{3} - CH(CH_{3})CH(CH_{3}) - CH_{3}\]

Step 5: 5. 2,3-Dimethylbutane

Lastly, this isomer has four carbon atoms in the longest chain, with two methyl groups branching off - one from the second and another from the third carbon atom: \[CH_{3} - CH(CH_{3}) - CH(CH_{3}) - CH_{3}\] So, these are all the five structural isomers possible for the alkane with the molecular formula C6H14.

Key Concepts

Isomerism in Organic Chemistry

Isomerism is a fascinating concept in organic chemistry where compounds have the same molecular formula but different structural arrangements, leading to varied physical and chemical properties. Structural isomers, in particular, are molecules that have the same molecular formula but differ in the connectivity of the atoms within the molecule. In other words, the skeleton of the molecular structure is rearranged, although the number of every atom involved remains the same.

For when it comes to alkanes, specifically, structural isomerism can be seen in the various ways carbon atoms can be connected to form different structures, ranging from straight chains to various branched forms. This unique property of carbon to form chains of varying lengths and shapes accounts for the diversity of organic compounds. Recognizing these different structural isomers is crucial, as it allows chemists to understand and predict the properties of organic substances in both nature and synthetic materials.

Structural Formula Representation

The structural formula of a compound provides a graphical representation that shows how atoms are arranged and bonded in a molecule. Unlike the molecular formula, which only gives the overall count of each type of atom, the structural formula illustrates the exact layout of the atoms. For education and clarity, it's crucial that the structural representation is simple and unambiguous.

Chemists use several types of structural formulas to depict molecules:

• The Lewis structure shows all the atoms and their bonds, and also includes lone pairs of electrons.
• The condensed structural formula groups together atoms that are bonded to a particular carbon, reducing the complexity of the image.
• Line-angle or skeletal formulas simplify the representation even further by only showing the bonds between carbon atoms, leaving out the carbon and hydrogen atoms for even clearer visualization.

By mastering the interpretation of these various representations, students can more effectively grasp the structures of even the most complex organic molecules.

Molecular Formula C6H14

When it comes to the molecular formula C6H14, the specific number of carbon (6) and hydrogen (14) atoms suggests that we are dealing with an alkane, a type of hydrocarbon consisting only of single bonds between the atoms. The alkanes are also known as saturated hydrocarbons, indicating that they have the maximum number of hydrogen atoms attached to the carbon chain, with no potential for additional bonds.

The exercise involving C6H14 illuminates the concept of isomerism by requiring the drawing of all possible structural isomers. This particular molecule has five isomers, each with a unique structural arrangement. The understanding and representation of these isomers are crucial for grasping the broader concepts of organic chemistry. As each isomer can have unique properties, being able to differentiate and represent these isomers correctly is of significant importance in both academic and practical chemistry settings.