Question

Draw the skeletal formula for each of the following: a. 1 -bromo-2-methylpentane b. methylcyclopropane c. ethylcyclohexane d. 4 -chlorooctane

Short answer

a. Br-CH2-CH(CH3)-CH2-CH2-CH3, b. cyclopropane with a CH3 group, c. cyclohexane with a CH2-CH3 group, d. CH3-CH2-CH2-CH(Cl)-CH2-CH2-CH2-CH3.

Step-by-step solution

Draw the Carbon Backbone for Compound a

Identify the main chain, which is pentane (5 carbons). Draw a straight chain of 5 carbon atoms.

Add Substituents for Compound a

Add a bromine (Br) at position 1 and a methyl (CH3) group at position 2 on the pentane chain.

Verify and Complete the Skeletal Formula for Compound a

Verify that the positions match the given name 1-bromo-2-methylpentane. The skeletal formula should have the structure: Br-CH2-CH(CH3)-CH2-CH2-CH3.

Draw the Carbon Backbone for Compound b

Identify the main structure, which is cyclopropane. Draw a triangle to represent the three-carbon ring.

Add Substituents for Compound b

Attach a methyl (CH3) group to the cyclopropane ring.

Verify and Complete the Skeletal Formula for Compound b

Ensure the methyl group is positioned properly on the cyclopropane ring. The skeletal formula should appear as a triangle with a line (representing the methyl group) extending from any of the vertices.

Draw the Carbon Backbone for Compound c

Identify the main structure, which is cyclohexane. Draw a hexagon to represent the six-carbon ring.

Add Substituents for Compound c

Attach an ethyl group (CH2-CH3) to the cyclohexane ring.

Verify and Complete the Skeletal Formula for Compound c

Ensure the ethyl group (CH2-CH3) is properly positioned on the cyclohexane ring. The skeletal formula should be a hexagon with an ethyl chain extending from any of the vertices.

Draw the Carbon Backbone for Compound d

Identify the main chain, which is octane (8 carbons). Draw a straight chain of 8 carbon atoms.

Add Substituents for Compound d

Add a chlorine (Cl) atom at position 4 on the octane chain.

Verify and Complete the Skeletal Formula for Compound d

Verify that the chlorine atom is correctly positioned at the 4th carbon atom of the chain. The skeletal formula should have the structure: CH3-CH2-CH2-CH(Cl)-CH2-CH2-CH2-CH3.

Key concepts

Understanding Alkanes

Alkanes are a fundamental class of organic compounds composed solely of carbon (C) and hydrogen (H) atoms. They are characterized by single bonds between carbon atoms, making them saturated hydrocarbons. This means each carbon atom forms four single bonds with either hydrogen or carbon atoms. A simple way to represent alkanes is using their general formula: \(\text{C}_n\text{H}_{2n+2}\) where \(n\) is the number of carbon atoms. Examples include methane (\(\text{CH}_4\)), ethane (\(\text{C}_2\text{H}_6\)), and pentane (\(\text{C}_5\text{H}_{12}\)). Alkanes are significant in chemistry due to their roles as fuels and starting materials for many industrial processes.

Cycloalkanes Simplified

Cycloalkanes are similar to alkanes but form a closed ring-like structure. This creates compounds with distinctive properties due to the ring strain and limited rotation around the carbon-carbon bonds. They follow the general formula \(\text{C}_n\text{H}_{2n}\) as they have two fewer hydrogen atoms compared to their linear counterparts. Common cycloalkanes include cyclopropane, with a triangle structure (3 carbons), and cyclohexane, with a hexagon structure (6 carbons). These rings can also have substituents attached, affecting their chemical behavior and reactions.

Role of Substituents in Organic Chemistry

Substituents are atoms or groups of atoms that replace hydrogen atoms in organic molecules. Understanding substituents is crucial for identifying and naming complex organic compounds. Common substituents include halogens (like chlorine and bromine), alkyl groups (such as methyl \(\text{CH}_3\) and ethyl \(\text{CH}_2\text{CH}_3\)). The position of substituents on the carbon chain or ring significantly impacts the properties and reactivity of the molecule. For example, in 1-bromo-2-methylpentane, '1-bromo' means a bromine atom is attached to the first carbon, and '2-methyl' signifies a methyl group on the second carbon.

Mastering IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) nomenclature system is a standardized method for naming organic compounds. This system ensures that each compound has a unique and universally understood name. The steps to name an organic molecule include:

• Identify the longest continuous carbon chain as the parent structure.
• Number the chain to give substituents the lowest possible positions.
• Name and number substituents, listing them alphabetically.
• Combine prefixes (for substituents), parent name, and suffix (for functional groups) in one name.

For example, in '4-chlorooctane,' 'octane' indicates eight carbons in the main chain, and '4-chloro' signifies a chlorine atom on the fourth carbon.