Question

Isooctane, 2,2,4 -trimethylpentane, is one of the possible structural isomers with the formula \(\mathrm{C}_{8} \mathrm{H}_{18} .\) Draw the structure of this isomer, and draw and name structures of two other isomers of \(\mathrm{C}_{8} \mathrm{H}_{18}\) in which the longest carbon chain is five atoms.

Short answer

Isooctane: 2,2,4-trimethylpentane. Other isomers: 2,3-dimethylpentane and 2-methylhexane.

Step-by-step solution

Understanding Isooctane Structure

Isooctane, or 2,2,4-trimethylpentane, has a parent chain of five carbon atoms. The structure includes three methyl groups attached at positions 2 and 4 on the main carbon chain, which makes this compound highly branched.

Drawing Isooctane

To draw isooctane: 1. Draw a straight chain of five carbon atoms. 2. Attach one methyl group (CH₃) to the second and fourth carbon atom of the main chain. 3. These branches make up the structure of isooctane.

Drawing Another Isomer with Longest Chain of Five

One possible structure is 2,3-dimethylpentane. To draw this structure: 1. Draw a five-carbon straight chain. 2. Attach a methyl group to the second and third carbon atoms of the chain to form 2,3-dimethylpentane.

Drawing a Second Isomer with Longest Chain of Five

Another possible structure is 2-methylhexane. To draw this: 1. Draw a five-carbon straight chain. 2. Attach an ethyl group (two carbon chain) to the second carbon atom of the straight chain, resulting in 2-methylhexane to maintain five carbon long main chain.

Naming the Isomers

The isomers are named based on IUPAC rules where the main chain is identified and substituents are named and numbered to give the smallest possible numbers. For the structures drawn: 2,2,4-trimethylpentane, 2,3-dimethylpentane, and 2-methylhexane are the correct names.

Key concepts

Isooctane

Isooctane is a specific structural isomer with the chemical formula \(\mathrm{C}_{8} \mathrm{H}_{18}\). Structural isomers are compounds that have the same molecular formula but different structural arrangements. With isooctane, the structure is characterized by a branched carbon chain. This particular isomer is also known formally as 2,2,4-trimethylpentane. The name indicates a main chain of five carbon atoms, with three additional methyl groups. These methyl groups are attached to the 2nd and 4th carbon of the main chain, which contributes to the high branching of the structure. Understanding branching is key. It influences the physical and chemical properties of the molecule, like boiling and melting points. Isooctane is noticeably used as a reference standard in petrol octane rating, signifying good combustion properties in engines.

IUPAC nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic way to name chemical compounds. IUPAC nomenclature allows chemists to identify and communicate about compounds unambiguously. For organic compounds like isomers of \(\mathrm{C}_{8} \mathrm{H}_{18}\), this involves a few specific rules:1. **Identify the longest carbon chain**: The base name is derived from the number of carbon atoms in this chain, using terms like "pentane" for five carbons.2. **Identify substituents**: Additional groups attached to this chain are noted, such as methyl (\(\mathrm{CH}_{3}\)) or ethyl (\(\mathrm{C}_{2}\mathrm{H}_{5}\)) groups.3. **Number the carbon atoms**: This ensures the smallest possible number is given to the substituents.4. **Assemble the name**: Combine the substituents and the main chain name, adjusting for placement such as "2,2,4-trimethylpentane".This systematic approach is essential for chemists to describe molecules even when encountering unknown or new compounds. It leads to a clearer understanding of the structural makeup of a substance.

Organic chemistry

Organic chemistry focuses on the study of carbon-containing compounds, which are the fundamental building blocks of life. This branch of chemistry explores how carbon atoms bond covalently with elements like hydrogen, oxygen, nitrogen, and other carbon atoms, forming a vast array of structures. In organic compounds, small changes in structure can lead to very significant differences in properties, behavior, and uses. This makes the study of structural isomers particularly important in understanding how such variations in molecular architecture provide different chemical properties. Organic chemistry is both intricate and fascinating due to the diversity and complexity of the compounds it addresses, ranging from simple molecules like methane to complex macromolecules such as DNA.

Carbon chain

A carbon chain forms the backbone of organic molecules, consisting of a series of carbon atoms bonded together. The length and branching of a carbon chain play crucial roles in defining the properties and characteristics of an organic molecule. - **Straight-chain isomers** have carbon atoms arranged in a linear sequence. - **Branched-chain isomers**, like isooctane, have one or more carbon atoms attached to the main chain as substituents. Carbon chains can vary widely in length and arrangement, leading to an immense variety of organic molecules. This flexibility allows carbon to create a nearly limitless variety of compounds, each with distinct properties. Understanding carbon chain variations is essential for grasping key concepts in organic chemistry, such as how structural isomers alter the physical and chemical properties of compounds.