Question

Give the the name or condensed structural formula, as appropriate:(c) 2 -methylheptane (d) 4 -ethyl- 2,3 -dimethyloctane (e) 1,2 -dimethylcyclohexane

Short answer

The condensed structural formulas are as follows: (c) 2-methylheptane: CH3-CH(CH3)-CH2-CH2-CH2-CH2-CH3 (d) 4-ethyl-2,3-dimethyloctane: CH3-CH(CH3)-CH(CH3)-CH(C2H5)-CH2-CH2-CH2-CH3 (e) 1,2-dimethylcyclohexane: For this compound, it's better to draw the structure instead of using a condensed formula. The structure has a cyclohexane ring with methyl groups at carbons 1 and 2.

Step-by-step solution

(Compound c: 2-methylheptane)

1. Identify the parent chain: In this case, it’s "heptane," indicating a 7-carbon chain. 2. Identify the substituent and its position: The substituent is a "methyl" group and its position is at carbon-2. 3. Write the condensed structural formula: We add the methyl group to the second carbon of the heptane chain. The condensed structural formula becomes: CH3-CH(CH3)-CH2-CH2-CH2-CH2-CH3.

(Compound d: 4-ethyl-2,3-dimethyloctane)

1. Identify the parent chain: The parent chain is "octane," indicating an 8-carbon chain. 2. Identify the substituents and their positions: The substituents are an "ethyl" group at carbon-4, and two "methyl" groups at carbons 2 and 3. 3. Write the condensed structural formula: We add the substituents to the corresponding carbon atoms in the octane chain. The condensed structural formula becomes: CH3-CH(CH3)-CH(CH3)-CH(C2H5)-CH2-CH2-CH2-CH3.

(Compound e: 1,2-dimethylcyclohexane)

1. Identify the parent chain: The parent chain is "cyclohexane," indicating a 6-carbon cyclic structure. 2. Identify the substituents and their positions: The substituents are two "methyl" groups at carbons 1 and 2. 3. Write the condensed structural formula: We add the methyl groups to the corresponding carbon atoms in the cyclohexane ring. The condensed structural formula becomes: CH3C(CH3)-CH₂-CH₂-CH₂-CH₂. In this case, we use a ring structure to represent the cyclohexane; so, it's better to draw the structure instead of using a condensed formula.

Key concepts

Hydrocarbon Nomenclature

In organic chemistry, hydrocarbon nomenclature is crucial for identifying and distinguishing different compounds. This naming system follows rules established by the International Union of Pure and Applied Chemistry (IUPAC).
The name is typically based on the longest continuous carbon chain that contains the highest-order functional group. To name a hydrocarbon:

• Find the longest chain in the molecule and use it as the parent chain's base name (like "heptane" for a 7-carbon chain).
• Identify and name attached groups, known as substituents (like "methyl" or "ethyl").
• Assign a number to each carbon atom in the main chain, beginning at the end closest to a substituent.
• Combine the substituents' names and numbers with the parent chain name, using hyphens and commas to separate numbers.

Understanding these rules helps create systematic names that clearly describe a molecule's structure.

Structural Formulas

A structural formula depicts the arrangement of atoms within a molecule. It provides a visual representation beyond mere chemical equations, showing how atoms connect.
There are several types of structural formulas:

• Condensed formulas, which present molecules in a line of text (e.g., CH3-CH2-CH3 for propane).
• Skeletal formulas, using lines to represent bonds between carbons and omitting hydrogen atoms for simplicity.
• Expanded formulas, showing all atoms and bonds in detail.

Condensed structural formulas, like CH3-CH(CH3)-CH2-CH2-CH2-CH2-CH3 for 2-methylheptane, summarize information efficiently and are commonly used in textbooks and academic papers.
Understanding structural formulas allows chemists to visualize molecules' shapes and highlights the importance of spatial arrangement in molecular interactions.

Cycloalkanes

Cycloalkanes are unique hydrocarbons, featuring carbon atoms arranged in a ring. These compounds are named similarly to straight-chain alkanes but with a "cyclo" prefix.
For example, cyclohexane has a six-carbon ring structure. Here are key features of cycloalkanes:

• The simplest cycloalkane is cyclopropane, with a three-carbon ring.
• They can feature ring strain due to non-linear bond angles.
• Small rings tend to have higher ring strain, influencing reactivity.

Understanding cycloalkanes' properties is essential, as their chemical behavior can significantly differ from their straight-chain counterparts due to ring strain and bond angles. Cycloalkanes are found throughout organic chemistry, including in substituted hydrocarbons like 1,2-dimethylcyclohexane, where additional groups are attached to the ring structure.

Substituted Hydrocarbons

Substituted hydrocarbons are formed when one or more hydrogen atoms in a hydrocarbon are replaced by other atoms or groups of atoms.
This modification greatly influences the compound's properties and reactivity. Key aspects include:

• Common substituents include alkyl groups (e.g., methyl, ethyl) and halogens (e.g., chlorine, bromine).
• Naming involves prefixing the substituent's names and positions to the base hydrocarbon name (e.g., 4-ethyl-2,3-dimethyloctane).
• Substituents can affect boiling points, solubility, and chemical reactivity.

By understanding substituted hydrocarbons, students grasp how minor structural changes can lead to significant shifts in chemical behavior. This concept is crucial in fields such as pharmacology and materials science, where specific molecule modifications result in desired properties.