Question

Draw the condensed structural formula for each of the following alkanes: (a) ethane (b) butane (c) hexane (d) octane

Short answer

(a) Ethane: \(CH_3CH_3\); (b) Butane: \(CH_3CH_2CH_2CH_3\); (c) Hexane: \(CH_3(CH_2)_4CH_3\); (d) Octane: \(CH_3(CH_2)_6CH_3\).

Step-by-step solution

Understanding Alkanes

First, recall that alkanes are hydrocarbons with only single bonds between carbon atoms. The general formula for alkanes is given by \(C_nH_{2n+2}\), where \(n\) is the number of carbon atoms. The name of an alkane provides information about its length based on prefixes: eth- (2 carbons), but- (4 carbons), hex- (6 carbons), and oct- (8 carbons).

Condensed Structural Formula for Ethane

Ethane has two carbon atoms. Using \(n = 2\) in the formula \(C_nH_{2n+2}\), we get \(C_2H_6\). Its condensed structural formula is \(CH_3CH_3\), indicating that each carbon is bonded to three hydrogen atoms.

Condensed Structural Formula for Butane

Butane consists of four carbon atoms. For \(n = 4\), \(C_nH_{2n+2}\) results in \(C_4H_{10}\). The condensed structural formula is \(CH_3CH_2CH_2CH_3\), which shows a continuous chain of four carbons with hydrogens completing their valency.

Condensed Structural Formula for Hexane

Hexane is composed of six carbon atoms. Substituting \(n = 6\) into \(C_nH_{2n+2}\) gives \(C_6H_{14}\). Its condensed structural formula is \(CH_3(CH_2)_4CH_3\), representing a straight chain of six carbon atoms.

Condensed Structural Formula for Octane

Octane features eight carbon atoms. Using \(n = 8\) in \(C_nH_{2n+2}\), we calculate \(C_8H_{18}\). The condensed structural formula is \(CH_3(CH_2)_6CH_3\), indicating a chain of eight carbons, where the interior carbon atoms are each connected to two hydrogen atoms.

Key concepts

Condensed Structural Formula

The condensed structural formula is an efficient way to represent the structure of alkanes without having to draw out each individual bond. It keeps the focus on the significant details by stringing together atoms in the order they are bonded, while omitting some of the explicit bond symbols. This method offers a cleaner and more straightforward depiction of molecules, especially useful for hydrocarbons, like alkanes, where the chains can become quite lengthy.

• An example of condensed structural formula is for ethane: instead of drawing each C-H bond, the formula is simply written as \(CH_3CH_3\).
• For longer alkanes, repetitive groups simplify further: hexane is written as \(CH_3(CH_2)_4CH_3\), highlighting repeated units.

Altogether, this approach helps in visualizing the molecule's backbone and understanding its chain length without the clutter of numerous bonds.

Hydrocarbons

Hydrocarbons are organic compounds composed entirely of hydrogen and carbon atoms. They serve as the fundamental building blocks for complex organic chemistry, forming the basic structure for various molecules. These compounds are primarily categorized into alkanes, alkenes, and alkynes based on the types of bonds present between the carbon atoms.

• Alkanes are the simplest form of hydrocarbons, containing only single bonds.
• They can appear as linear chains, branched structures, or even as rings.

Their general formula, \(C_nH_{2n+2}\), helps to predict the number of hydrogen atoms for a particular number of carbon atoms. Recognizing this basis helps in constructing the molecular structure or predicting properties of alkanes.

Single Bonds

Single bonds play a foundational role in the structure of alkanes, which are saturated hydrocarbons. In chemistry, a single bond is formed when two atoms share one pair of valence electrons, creating the most basic type of chemical bond. This characteristic is critical in alkanes as it dictates the molecule's shape and stability.

• Single bonds allow carbon atoms to rotate around the bond axis, providing these molecules flexibility.
• Furthermore, they make alkanes more chemically stable than other hydrocarbons due to the lack of additional reactive sites.

This single bond characteristic leads to the specific naming of these compounds as 'saturated', completely filled with hydrogen atoms, distinguishing them from alkenes and alkynes.

Carbon Atoms

Carbon atoms form the backbone of all organic molecules, including the uncomplicated structures of alkanes. Each carbon has the capacity to create four bonds, allowing for complex configurations and immense variability within hydrocarbon structures.

• They can connect in long chains or branch out into intricate shapes, influencing the properties of the hydrocarbon.
• This tetravalence is the reason hydrocarbons, such as alkanes, can form so many possible substances.

The presence and organization of carbon atoms in alkanes dictate many physical and chemical properties, such as boiling points, solubility, and reactivity. In essence, they are the cornerstone of organic chemistry and invaluable for understanding molecular arrangements and transformations.