Question

Propose structures and give IUPAC names for the following: (a) A diethyldimethylhexane (b) \(A\) (3-methylbutyl)-substituted alkane

Short answer

a) 2,3-diethyl-2,4-dimethylhexane; b) 3-(3-methylbutyl)nonane.

Step-by-step solution

Understand the Structure for Diethyldimethylhexane

We need a hexane backbone with two ethyl and two methyl groups attached. The longest chain is six carbons, with four substituents needing placement.

Assign Positions for Substituents on Hexane

Assign numbers to the hexane chain from 1 to 6. Two ethyl groups could be placed at positions 2 and 3, and methyl groups could be placed at positions 2 and 4: this forms 2,3-diethyl-2,4-dimethylhexane.

Ensure IUPAC Naming Is Correct

Verify the substituents align with IUPAC rules. The names of the substituents: 2,3-diethyl-2,4-dimethyl. The main chain, hexane, identifies the location and type of each group.

Understand the Structure for a (3-methylbutyl) Substituted Alkane

This includes a main alkane chain, with a substituent group called 3-methylbutyl attached to it. Determine the main alkane onto which this group will attach.

Determine a Suitable Main Alkane

Choose a simple straight-chain alkane, such as nonane, onto which the 3-methylbutyl group can attach at a specific position. This leads to a name like 3-(3-methylbutyl)nonane.

Finalize the IUPAC Names

For a): 2,3-diethyl-2,4-dimethylhexane, and for b): 3-(3-methylbutyl)nonane.

Key concepts

Alkane Structure

Alkanes are the simplest type of organic compounds known as hydrocarbons, consisting entirely of single-bonded carbon and hydrogen atoms. The general formula for alkanes is \( C_nH_{2n+2} \), where \( n \) is the number of carbon atoms. The structure can be either a straight or branched chain. For example, hexane is an alkane with a straight-chain structure and consists of 6 carbon atoms interconnected, forming a continuous chain with hydrogen atoms completing each carbon's valency.
In organic chemistry, understanding the basic structure of alkanes helps in determining how different substituents can be added to form more complex molecules. The primary carbon chain is often referred to as the parent chain, and it serves as the skeleton upon which various substituents are positioned.

Substituents in Organic Molecules

Substituents in organic chemistry refer to atoms or groups of atoms that are attached to the main chain of a molecule. They can significantly alter the properties and naming of the compound. Common substituents include groups like methyl \(-CH_3 \), ethyl \(-C_2H_5 \), and propyl \(-C_3H_7 \), which are derived from alkanes by removing one hydrogen atom.
Identifying and understanding substituents is critical when performing IUPAC naming, as they are often highlighted as prefixes in the compound’s name. Placement and type of substituents must be considered carefully, as different placements can lead to different structural isomers, each having its own distinctive properties.
For example, in diethyldimethylhexane, the substituents are two ethyl and two methyl groups, which are attached to the hexane chain. These substituents not only influence the chemical name but also can dictate the molecular geometry and polarity of the compound.

Organic Chemistry Problem-Solving

Problem-solving in organic chemistry often involves understanding the molecular structure and then applying logical reasoning to deduce functional groups, presence of substituents, and overall molecular shape. When presented with a problem, start by identifying the basic structure - like the parent hydrocarbon chain - and then note any branches or substituents.
It can be helpful to draw the molecule, placing substituents at various positions to determine the most stable and accurate structure. Practice naming from basic to complex compounds enables students to better analyze and solve complex problems. Break down the problem into smaller steps: first determine the longest carbon chain, then identify and position substituents, and finally, check the IUPAC naming.
Consider the solved example of 2,3-diethyl-2,4-dimethylhexane: through a structured approach, you learn to position substituents and verify correctness systematically.

IUPAC Rules for Naming Alkanes

The IUPAC system provides a standardized method for naming organic compounds. It ensures clarity and consistency in the identification of molecules. For alkanes, follow these basic naming rules:
1. **Identify the Longest Chain:** Determine the longest continuous chain of carbon atoms, which becomes the base (parent) name of the molecule (e.g., hexane for a six-carbon chain).
2. **Number the Chain:** Assign numbers to the carbon atoms in the main chain beginning from the end nearest to a substituent to ensure the substituents have the lowest possible numbers.
3. **Name and Locate Substituents:** Identify all substituents attached to the main chain. Prefix their positions on the chain to their names (e.g., 2-methyl, 4-ethyl).
4. **Compile the Name:** Combine the names of the substituents and the parent hydrocarbon chain into a full name, listing substituents in alphabetical order and adding prefixes like di-, tri-, etc., for multiple identical groups.
Using these rules, the names 2,3-diethyl-2,4-dimethylhexane and 3-(3-methylbutyl)nonane can be confidently assigned, ensuring proper chemical identification.