Question

Give the isomers of the carboxylic acid with the molecular formula \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\).

Short answer

The two isomers are butanoic acid and methyl propanoate.

Step-by-step solution

Identify the main functional group and core structure

A carboxylic acid has a -COOH functional group. With 4 carbons in the molecular formula, first consider a straight-chain structure with the carboxylic acid at one end.

Experiment with Different Arrangements

Next, experiment with arranging the functional group in different places along this skeleton. Because a carboxylic acid functional group must be at the end of a chain, this functional group could also be located in the second carbon atom from the end.

Identify Isomers

Results in two isomers: \[ \begin{array}{ll} 1) & \text { Butanoic acid: }-\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{COOH} \ 2) & \text { Methyl propanoate: }-\mathrm{CH}_{3}-\mathrm{CH}-\left(\mathrm{CH}_{3}\right)-\mathrm{COOH} \end{array}\] Note: Isomers also be cyclical in structure, but for a carboxylic acid with only four carbon atoms, a cyclic structure is not possible.

Key concepts

Molecular Structure of Carboxylic Acids

Understanding the molecular structure is crucial when working with carboxylic acids. These compounds contain a specific functional group, written as -COOH, that defines their chemical properties. The molecular formula for a carboxylic acid with four carbon atoms is \(\mathrm{C}_4\mathrm{H}_8\mathrm{O}_2\). This formula indicates that the compound contains four carbon atoms, eight hydrogen atoms, and two oxygen atoms.

In organic chemistry, the arrangement of these atoms is equally important as their number. These atoms are bonded in specific geometries that determine the overall structure of the compound. For carboxylic acids, the -COOH group is a distinguishing feature. It consists of a carbon double-bonded to an oxygen (forming a carbonyl group) and single-bonded to an OH group. This must be attached to the chain's end in a simple linear carboxylic acid, influencing its potential isomers.

Functional Groups in Carboxylic Acids

A functional group refers to a specific group of atoms within a molecule that is primarily responsible for the characteristic reactions and properties of the compound. In carboxylic acids, the key functional group is the carboxyl group (-COOH). This group is not only reactive but also polar, allowing carboxylic acids to form hydrogen bonds with other molecules.

This characteristic increases the solubility of carboxylic acids in water, particularly those with shorter carbon chains. The carboxyl group combines the properties of carbonyl (C=O) and hydroxyl (OH) groups, making carboxylic acids versatile in chemical reactions. Understanding how these functional groups interact within a molecule is essential when identifying carboxylic acid isomers and their behavior in various reactions.

Isomer Identification

Isomer identification involves recognizing different structural formulas that share the same molecular formula. For carboxylic acids with a form of \(\mathrm{C}_4\mathrm{H}_8\mathrm{O}_2\), two main types of isomers can exist: structural and stereoisomers. However, stereoisomers are not considered here.

In our context, structural isomers have the same number of each type of atom but differ in the connectivity of the atoms within the molecule. For the given molecular formula, these isomers are:

• Butanoic acid (straight-chain isomer): connects all the carbon atoms in a continuous line with the -COOH at the end.
• Methyl propanoate (a branched-chain isomer): rearranges the carbon atoms to form a branch, still incorporating the -COOH group, but with different carbon connectivity.

This ability to form different structures with the same formula is crucial in organic chemistry, as each form can have unique properties.

Exploring Organic Chemistry

Organic chemistry is a vast field of study dedicated to the investigation of carbon-based compounds, their structures, properties, and reactions. Carboxylic acids are a fundamental class within organic chemistry known for their diverse roles in biological and industrial processes.

Studying organic chemistry involves comprehending how molecular structure affects a compound's properties. This includes the understanding of bonding, reactivity, and the spatial arrangement of atoms. In addition, it requires analyzing how different functional groups alter a compound's characteristics and behavior during chemical reactions.

Students of organic chemistry learn to predict how changes in molecular structure or functional group placement might affect a molecule’s overall chemistry. This level of understanding is particularly important when identifying isomers and attempting to discern how these differences may affect their utility and behavior in practical applications.