Question

Draw the structure of each of the following compounds: (a) 2,2 -dimethylpentane (b) 3,3 -diethylpentane (c) 3-ethyl-2-methylpentane (d) 3 -ethylhexane

Short answer

Use the compound names to guide structure drawing: identify the longest chain and attach groups at specified positions.

Step-by-step solution

Understand the Nomenclature

The name of the compound gives us clues about the structure: - The base name, such as 'pentane' or 'hexane,' indicates the number of carbon atoms in the longest chain. 'Pentane' means a chain of five carbons, while 'hexane' means six carbon atoms. - The numbered prefixes before the base name (like 2,2- or 3,3-) tell us where the branches are located on the carbon chain. - The term 'dimethyl' or 'diethyl' indicates the type and number of identical groups attached to the main chain. 'Methyl' means a -CH3 group, and 'ethyl' is a -CH2CH3 group.

Draw 2,2-Dimethylpentane

Start with the longest continuous chain: - Draw a chain of five carbon atoms (pentane: C1-C2-C3-C4-C5). - According to the name (2,2-dimethyl), place two methyl (-CH3) groups on the second carbon. Your structure should look like this: CH3 | CH3-C-CH2-CH2-CH3 | CH3

Draw 3,3-Diethylpentane

Build the base structure: - Draw a five-carbon chain (C1-C2-C3-C4-C5). - Attach two ethyl groups (C2H5) on the third carbon as indicated by the name (3,3-diethyl). The structure will appear as: CH2CH3 | CH3-CH2-C-CH2-CH3 | CH2CH3

Draw 3-Ethyl-2-Methylpentane

Design the molecular structure: - Start with a five-carbon chain (pentane: C1-C2-C3-C4-C5). - Place an ethyl group (-CH2CH3) on the third carbon. - Add a methyl group (-CH3) on the second carbon. The resulting structure: CH2CH3 | CH3-CH-C-CH2-CH3 | CH3

Draw 3-Ethylhexane

Create the hexane structure: - Begin with a six-carbon chain (hexane: C1-C2-C3-C4-C5-C6). - Add an ethyl group (-CH2CH3) on the third carbon as specified by the 3-ethyl prefix. The final structure should look like: CH2CH3 | CH3-CH-C-CH2-CH2-CH3

Key concepts

Nomenclature

In organic chemistry, nomenclature is like a special naming system for chemicals, ensuring everyone can identify the same substance. Each name corresponds to a unique structure, guiding chemists in understanding the components and their arrangement. Here's how it breaks down:

• The base name, such as 'pentane' or 'hexane,' tells us about the longest carbon chain. 'Pentane' means there are five carbon atoms in a row, 'hexane' means six.
• Prefixes like 2,2- or 3,3- reveal the position of any branches on this chain. They indicate which carbon atom these branches connect to.
• 'Dimethyl' or 'diethyl' specifies what kind of branches are attached and their number. 'Methyl' means a \( ext{-CH}_3 \) group, while 'ethyl' refers to a \( ext{-CH}_2 ext{-CH}_3 \) group.

Nomenclature is crucial for both communication and understanding in organic chemistry. It is what allows us to draw molecular structures from names.

Alkanes

Alkanes are a family of compounds in organic chemistry. They are simple hydrocarbons, which means they are made up entirely of carbon (C) and hydrogen (H) atoms. Here are some key features:

• Alkanes are saturated, meaning they have single bonds only. Every carbon atom forms four bonds, either with other carbons or with hydrogens.
• The molecular formula for alkanes follows a pattern: \( ext{C}_n ext{H}_{2n+2} \) where \( n \) is the number of carbon atoms.
• They form the simplest structure known as "straight chains," but can also exist in branched forms, increasing their complexity and variety.

Understanding alkanes provides a foundation for studying more complex hydrocarbons and their reactions, making them an essential part of organic chemistry.

Structural Formula

A structural formula is a diagram that shows us the exact layout of the atoms in a molecule. Instead of just listing the number of each atom, it reveals their arrangement. Let's delve into why structural formulas are important:

• They show the connectivity between atoms, crucial for understanding molecular behavior and reactivity.
• This type of formula can represent different forms like straight chains, branched chains, or even rings.
• For example, 2,2-dimethylpentane shows a five-carbon chain with branches coming off the second carbon, making the arrangement clear.

Structural formulas are essential in organic chemistry because they allow visual representation of molecular structures, helping chemists predict how molecules might interact or transform during reactions.

Carbon Chain

The carbon chain is the backbone of organic molecules, composed of carbon atoms linked together. Its length and structure influence the properties of organic compounds. Here’s more about carbon chains:

• The length of a carbon chain determines the molecule's base name, like 'pentane' for five carbons or 'hexane' for six.
• Carbon chains can be straight, meaning all carbons are in a line, or branched, where one or more carbons stick out from the main line.
• Branching affects everything from the molecule's boiling point to its chemical reactivity, because it alters how closely molecules can pack together.

Understanding the concept of carbon chains helps in predicting and explaining the behavior of various organic compounds, making it a fundamental topic in organic chemistry.