Question

Without looking back at the text, draw structural formulas and give the common names for the three isomers of pentane, \(\mathrm{C}_{5} \mathrm{H}_{12}\).

Short answer

The three isomers of pentane, their structural formulas, and their common names are: 1. \(n\)-Pentane: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 2. Isopentane: \(\mathrm{CH}_{3}-\mathrm{CH}( \mathrm{CH}_{3})-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 3. Neopentane: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}(\mathrm{CH}_{3})-\mathrm{CH}_{3}\)

Step-by-step solution

Identify the Main Carbon Chain for Each Isomer

We need to find the different possible arrangements of carbon atoms that result in isomers having the same molecular formula \(\mathrm{C}_{5} \mathrm{H}_{12}\). The carbon atoms can either be arranged in a straight chain or in a branched chain. There are three possible configurations: 1. A straight chain with 5 carbon atoms. 2. A branch at the second carbon atom in a 4-carbon chain. 3. A branch at the third carbon atom in a 4-carbon chain.

Draw the Structural Formulas for Each Isomer

Based on the different possible carbon chain arrangements identified in Step 1, we can now draw the structural formulas for each isomer. 1. The straight-chain isomer: \[ \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3} \] 2. The branched isomer with a branch at the second carbon atom: \[ \mathrm{CH}_{3}-\mathrm{CH}( \mathrm{CH}_{3})-\mathrm{CH}_{2}-\mathrm{CH}_{3} \] 3. The branched isomer with a branch at the third carbon atom: \[ \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}(\mathrm{CH}_{3})-\mathrm{CH}_{3} \]

Name Each Isomer

Now, we'll assign the common names to each of the structural isomers of pentane: 1. Straight-chain isomer: \(n\)-Pentane 2. Branched isomer with a branch at the second carbon atom: Isopentane 3. Branched isomer with a branch at the third carbon atom: Neopentane So, the three isomers of pentane, their structural formulas, and their common names are as follows: 1. \(n\)-Pentane: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 2. Isopentane: \(\mathrm{CH}_{3}-\mathrm{CH}( \mathrm{CH}_{3})-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 3. Neopentane: \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}(\mathrm{CH}_{3})-\mathrm{CH}_{3}\)

Key concepts

Structural Formulas

The structural formula of a molecule is a graphical representation that conveys the arrangement of atoms and the bonds between them. When it comes to hydrocarbons, like pentane designated by the molecular formula \(\text{C}_{5} \text{H}_{12}\), the structural formula provides a clear picture of how the carbon (C) and hydrogen (H) atoms are organized. In the context of isomers, the structural formula is particularly crucial as it shows how the same molecular formula can result in different arrangements, leading to distinct compounds with unique properties.

Think of a structural formula as a floor plan for a building – it shows which rooms (atoms) are connected and how. For students, visualizing these connections is essential for understanding organic chemistry. The drawn structures for the isomers of pentane allow us to appreciate the different possibilities: a straight chain, a branch at the second carbon, and another at the third carbon, each creating distinctly different isomers with their set of properties.

Organic Isomers

Isomerism in organic chemistry plays a fundamental role in the diversity of organic compounds. Organic isomers are compounds that share the same molecular formula but differ in the arrangement of their atoms or in the orientation of those arrangements in space. There are two main types of isomerism: structural isomerism and stereoisomerism. For pentane \(\text{C}_{5} \text{H}_{12}\), which falls under the category of alkanes, we are concerned specifically with structural isomerism.

This type of isomerism includes chain isomerism (differences in the main carbon chain), positional isomerism (differences in the position of functional groups), and functional group isomerism (different functional groups formed). The case with pentane showcases chain isomerism, where the carbon chain configuration results in three different isomers: n-pentane, isopentane, and neopentane. It's like rearranging the same pieces of a puzzle to form differing pictures – all made from the same pieces but organized uniquely.

Carbon Chain Configurations

Carbon chain configurations are at the heart of organic isomerism. A carbon chain can be linear or branched and extends from the simplest of hydrocarbons (methane) to complex molecular structures in bigger organic molecules. In the configuration of pentane isomers, the shape and structure of the carbon backbone are pivotal to their chemical identities.

In a straight-chain configuration, like n-pentane, all carbon atoms are connected in a row without branches. However, branches introduce diversity; for example, isopentane has a methyl group (\(\text{CH}_{3}\)) branching off the second carbon, and neopentane is even more branched with two methyl groups extending from a central carbon.

These configurations not only determine the isomers' names but also affect physical and chemical properties such as boiling points, reactivities, and how these molecules interact with other substances. In essence, carbon chain configurations in organic chemistry are the blueprints determining the vast array of structures and functions of organic molecules. For students, mastering how to visualize and draw these configurations is like learning to read the alphabet of organic chemistry.