Question

For each of the following straight-chain alkanes, draw the structural formula. a. ethane b. butane c. hexane

Short answer

\(Ethane: \newline H-H \newline | | \newline C-C \newline | | \newline H-H \newline \newline Butane: \newline H H H H \newline | | | | \newline C-C-C-C \newline | | | | \newline H H H H \newline \newline Hexane: \newline H H H H H H \newline | | | | | | \newline C-C-C-C-C-C \newline | | | | | | \newline H H H H H H \)

Step-by-step solution

(Draw Ethane's Structural Formula)

Ethane has the molecular formula C2H6. To draw the structural formula, we start with two carbon atoms and form a single bond between them. Each carbon atom then forms three more single bonds with hydrogen atoms, resulting in a total of six hydrogen atoms. The structural formula for ethane is, therefore: H H | | C-C | | H H

(Draw Butane's Structural Formula)

Butane has the molecular formula C4H10. To draw the structural formula, we start with four carbon atoms and form single bonds between them in a chain. Each of the two end carbon atoms forms three more single bonds with hydrogen atoms. The two middle carbon atoms form two more single bonds with hydrogen atoms each, resulting in a total of ten hydrogen atoms. The structural formula for butane is: H H H H | | | | C-C-C-C | | | | H H H H

(Draw Hexane's Structural Formula)

Hexane has the molecular formula C6H14. To draw the structural formula, we start with six carbon atoms and form single bonds between them in a chain. Each of the two end carbon atoms forms three more single bonds with hydrogen atoms. The four middle carbon atoms form two more single bonds with hydrogen atoms each, resulting in a total of fourteen hydrogen atoms. The structural formula for hexane is: H H H H H H | | | | | | C-C-C-C-C-C | | | | | | H H H H H H

Key concepts

Drawing Structural Formulas

When it comes to visualizing molecules in organic chemistry, learning how to draw structural formulas is fundamental. A structural formula is essentially a blueprint of a molecule, highlighting not only what atoms are present but also how they are connected. For alkanes, which are hydrocarbons with only single bonds, the procedure is pretty straightforward.

To begin drawing the structural formula for an alkane, identify the number of carbon atoms and hydrogen atoms present in its molecular formula. Then, represent each carbon atom with a 'C' and place them in a sequential chain, connecting them with single lines which stand for single covalent bonds. Finally, add the hydrogen atoms, 'H', ensuring that each carbon atom forms four bonds in total, following the tetravalency of carbon. This approach was taken in the textbook solutions to illustrate ethane, butane, and hexane.

For example, ethane (C₂H₆) is drawn with two carbon atoms bonded together with single lines to three hydrogen atoms each. Butane's structure extends this process, connecting four carbon atoms in a row with hydrogens filling in to satisfy the bonding criteria. The step-by-step method provided makes it easier to visualize the molecular structure and is a critical skill for anyone studying organic chemistry.

Chemical Representation of Alkanes

Alkanes are the simplest type of organic compounds, consisting of carbon and hydrogen atoms with single bonds. The chemical representation of alkanes using structural formulas serves to help students understand the molecular layout of these compounds.

The general formula for alkanes is C_nH_2n+2, where 'n' is the number of carbon atoms. This formula implies the saturation of carbon-carbon bonds in alkanes—each carbon atom can form four bonds, typically filled by hydrogen atoms when considering straight-chain alkanes. Strategies in the textbook solution illustrate the carbon backbone as a straight line of bonded 'C' atoms with 'H' atoms branching off.

Converting a molecular formula, such as C₄H₁₀ for butane, to its structural representation involves insight into this bonding pattern, making it simpler for students to comprehend how changing the number of carbon atoms affects the overall structure and hydrogen count. Recognizing patterns in such representations is crucial for predicting physical and chemical properties of alkanes.

Organic Chemistry Basics

Understanding the basics of organic chemistry starts with a grasp of the significant types of hydrocarbon compounds, amongst which alkanes play a pivotal role. These are characterized by having only single covalent bonds between carbon atoms, differentiating them from alkenes and alkynes, which include double and triple bonds respectively.

The foundational concepts lie in appreciating the tetrahedral geometry of carbon, the idea of homologous series where compounds differ by a CH₂ unit, and isomerism which occurs when molecules have the same molecular formula but different structural arrangements. The textbook solutions for drawing the structural formulas of straight-chain alkanes are grounded on these basics. From the provided steps for ethane, butane, and hexane, it is evident that the molecular structure expands with each additional CH₂ unit, while maintaining a similar bonding pattern.

Hence, as students progress in organic chemistry, they will build upon these fundamentals to tackle more complex molecules and reactions, emphasizing the importance of a solid understanding of these basic concepts in order to succeed in the field.