Question

For each of the following numbers of carbon atoms, give the structure of the straight-chain alkane with that number of carbon atoms, and give its name. a. eight carbon atoms b. six carbon atoms c. four carbon atoms d. five carbon atoms

Short answer

a. The structure of the straight-chain alkane with eight carbon atoms is CH₃(CH₂)₆CH₃, and its name is "Octane". b. The structure of the straight-chain alkane with six carbon atoms is CH₃(CH₂)₄CH₃, and its name is "Hexane". c. The structure of the straight-chain alkane with four carbon atoms is CH₃CH₂CH₂CH₃, and its name is "Butane". d. The structure of the straight-chain alkane with five carbon atoms is CH₃(CH₂)₃CH₃, and its name is "Pentane".

Step-by-step solution

Draw the structure

Draw a straight chain of 8 carbon atoms, each bonded to hydrogen atoms. The carbon atoms at the ends will have three hydrogen atoms while the remaining ones in the middle will have two hydrogen atoms each.

Determine the IUPAC name

The IUPAC name for an alkane with 8 carbon atoms is "Octane". b. Six carbon atoms

Draw the structure

Draw a straight chain of 6 carbon atoms, each bonded to hydrogen atoms. The carbon atoms at the ends will have three hydrogen atoms while the remaining ones in the middle will have two hydrogen atoms each.

Determine the IUPAC name

The IUPAC name for an alkane with 6 carbon atoms is "Hexane". c. Four carbon atoms

Draw the structure

Draw a straight chain of 4 carbon atoms, each bonded to hydrogen atoms. The carbon atoms at the ends will have three hydrogen atoms while the remaining ones in the middle will have two hydrogen atoms each.

Determine the IUPAC name

The IUPAC name for an alkane with 4 carbon atoms is "Butane". d. Five carbon atoms

Draw the structure

Draw a straight chain of 5 carbon atoms, each bonded to hydrogen atoms. The carbon atoms at the ends will have three hydrogen atoms while the remaining ones in the middle will have two hydrogen atoms each.

Determine the IUPAC name

The IUPAC name for an alkane with 5 carbon atoms is "Pentane".

Key concepts

IUPAC naming system

The IUPAC naming system provides a standardized method for naming chemical compounds. It's like a universal language that allows chemists to identify substances in a predictable manner.
This systematic approach helps avoid confusion, especially with organic compounds, which can have several names depending on structure and function.
For alkanes, the naming process is both simple and logical. Here's how it works:

• Identify the longest carbon chain in the molecule. This will give you the base name (e.g., methane, ethane, propane, etc.).
• Number the carbon atoms in the main chain, starting from the end nearest to any branches or functional groups.
• Add any substituents as prefixes, with their position indicating on which carbon they are attached.
• Use suffixes like "-ane" for alkanes, where all carbons are single-bonded.

For example, for a straight-chain alkane with six carbon atoms, we have "hex" from Greek and Latin roots for six, and "ane" for alkane, resulting in "hexane." This systematic approach ensures clarity and uniformity in chemical nomenclature.

Straight-chain hydrocarbons

Straight-chain hydrocarbons, also known as normal alkanes, are a type of alkane where carbon atoms are connected in a linear sequence with no branches.
These structures are composed solely of carbon and hydrogen atoms. By arranging carbon atoms in this linear fashion, each carbon forms a single bond with two other carbon atoms in the chain, except for the terminal carbons, which connect to three hydrogen atoms.
The simplicity of straight-chain hydrocarbons is their defining trait:

• They are saturated with hydrogen, which means they contain only single bonds, ensuring stability.
• They provide a baseline structure for more complex hydrocarbons that can feature branches or rings.

Straight-chain hydrocarbons serve as excellent examples in learning the basics of organic chemistry because of their predictable naming and straightforward molecular configuration. For instance, in a straight-chain hydrocarbon with eight carbon atoms, named "octane," the carbon atoms are lined up in such a way that the structure maintains its simple, unbranched form.

Carbon and hydrogen bonding

Carbon and hydrogen bonding is fundamental to organic chemistry, as these bonds form the backbone of alkanes and many other organic compounds.
Understanding these bonds is essential for grasping how organic molecules are constructed and interact. Carbon atoms can form four covalent bonds, allowing them to bond with up to four other atoms simultaneously. In alkanes:

• Each carbon atom bonds with hydrogen or other carbon atoms through single covalent bonds.
• The simplest carbon bond with hydrogen is found in methane, where a single carbon atom bonds with four hydrogen atoms.
• In more complex alkanes, like pentane or hexane, carbon atoms bond with each other in a chain, forming a stable covalent bond network.

These strong single bonds contribute to the chemical stability of alkanes. This stability, combined with saturated carbon atoms, means alkanes are generally less reactive, which is why they are often used as fuels and lubricants in industry.