Question

Write structural formulas for the following alkanes. (a) 2,2,4 -trimethylpentane (b) 2,2 -dimethylpropane (c) 4 -isopropyloctane (d) 2,3,4 -trimethylheptane

Short answer

Answer: There are three methyl groups attached to the main chain in 2,2,4-trimethylpentane, and they are attached at positions 2, 2, and 4.

Step-by-step solution

Identify the main carbon chain

The main chain has 5 carbon atoms, as indicated by the word "pentane."

Identify the attached groups

There are three methyl groups attached to the main chain, as indicated by the prefix "trimethyl."

Place the attached groups according to their positions

Methyl groups are attached at positions 2, 2, and 4, as given in the name of the compound.

Draw the structural formula

Here is the structural formula for 2,2,4-trimethylpentane: (CH3)3C-C(CH3)2-C3H7 (b) 2,2-dimethylpropane

Identify the main carbon chain

The main chain has 3 carbon atoms, as indicated by the word "propane."

Identify the attached groups

There are two methyl groups attached to the main chain, as indicated by the prefix "dimethyl."

Place the attached groups according to their positions

Methyl groups are attached at position 2, as given in the name of the compound.

Draw the structural formula

Here is the structural formula for 2,2-dimethylpropane: CH3-C(CH3)2-CH3 (c) 4-isopropyloctane

Identify the main carbon chain

The main chain has 8 carbon atoms, as indicated by the word "octane."

Identify the attached group

There is an isopropyl group attached to the main chain at position 4, as given in the name of the compound.

Place the attached group according to its position

The isopropyl group is attached at position 4, as given in the name of the compound.

Draw the structural formula

Here is the structural formula for 4-isopropyloctane: CH3-CH2-CH2-CH(CH3)2-CH2-CH2-CH2-CH3 (d) 2,3,4-trimethylheptane

Identify the main carbon chain

The main chain has 7 carbon atoms, as indicated by the word "heptane."

Identify the attached groups

There are three methyl groups attached to the main chain, as indicated by the prefix "trimethyl."

Place the attached groups according to their positions

Methyl groups are attached at positions 2, 3, and 4, as given in the name of the compound.

Draw the structural formula

Here is the structural formula for 2,3,4-trimethylheptane: CH3-CH(CH3)-CH(CH3)-C(CH3)2-CH2-CH2-CH3

Key concepts

Understanding Organic Chemistry

Organic chemistry is the scientific study of the structure, properties, and reactions of organic compounds and organic materials—substances that contain carbon atoms. Understanding organic chemistry is crucial for a range of scientific disciplines, including pharmaceuticals, petrochemicals, and biochemistry. It starts with the basic building blocks—hydrocarbons, which are compounds solely made up of hydrogen and carbon atoms. Alkanes are the simplest form of hydrocarbons, characterized by single covalent bonds between carbon atoms, and follow a general formula of \(C_nH_{2n+2}\).

Alkanes are saturated hydrocarbons, meaning they contain the maximum possible number of hydrogen atoms per carbon, creating a structure with no double or triple bonds—only single bonds. This property of alkanes makes them relatively less reactive, providing a good foundation for understanding more complex organic reactions that involve unsaturated hydrocarbons such as alkenes and alkynes, which have double and triple bonds, respectively.

Navigating Alkane Nomenclature

The nomenclature of alkanes is based on a set of rules established by the International Union of Pure and Applied Chemistry (IUPAC). These rules allow chemists to concisely communicate complex structures through names. For alkanes, the name typically starts with a prefix indicating the number of carbon atoms in the longest continuous chain (for example, 'meth-' for one carbon, 'eth-' for two, and so forth), followed by the suffix '-ane' which identifies the molecule as an alkane.

Substituents, or branches, off the main carbon chain are prefixed with their specific names and numbers to indicate their positions on the main chain. It's important to number the carbon atoms in a way that gives the substituents the lowest possible numbers, which can be seen in our examples like 2,2,4-trimethylpentane or 4-isopropyloctane. The exercise of writing structural formulas for different alkanes provides critical practice in applying IUPAC nomenclature rules, enhancing one's ability to both name and understand the structure of organic compounds.

Chemical Structure Representation of Alkanes

Representing the chemical structure of alkanes involves creating visual models that accurately depict the spatial arrangement of atoms within the molecule. These can be simple line or 'stick' drawings that show the carbon backbone and any attached hydrogen atoms or substituent groups. It is crucial for these representations to clearly define the placement of each atom and their bonds, as in the step-by-step solutions for drawing structural formulas of the given alkanes.

The accurate representation of the molecular structure is essential not only for identifying the molecule but also for understanding its potential chemical reactions. Working through examples like 2,2-dimethylpropane or 2,3,4-trimethylheptane from textbook exercises helps students to better visualize and thus comprehend how these molecules are constructed and how they might interact in various chemical environments.