Problem 76 - General Chemistry: Principles and Modern Applications

Question

Which of the following names is most appropriate for the molecule \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH} ?\) (a) dimethyleneacetic acid; (b) propanoic acid; (c) butanoic acid; (d) oxobutylalcohol.

Step-by-Step Solution

Answer

The most appropriate name for the molecule \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH}\) is butanoic acid.

Step 1: Identify the functional group

The molecule \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH}\) contains a carboxylic acid group (\(\mathrm{COOH}\)). Therefore, it belongs to the carboxylic acid class of organic compounds.

Step 2: Number of carbon atoms

Next, determine the total number of carbon atoms in the longest carbon chain. The molecule \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{COOH}\) has four carbon atoms in its longest chain, including the carboxylic acid carbon.

Step 3: Determine the appropriate IUPAC name

Based on IUPAC nomenclature, carboxylic acids are named as 'alkanoic acids'. The prefix 'alkan-' refers to the number of carbon atoms in the longest chain. For four carbons, the prefix 'butan-' is used. Thus, the molecule is named 'butanoic acid'.

Key Concepts

Carboxylic Acids

Carboxylic acids are an important class of organic compounds. They contain a specific functional group known as the carboxyl group (\(\mathrm{COOH}\)). This functional group is characterized by a carbonyl group (\(\mathrm{C=O}\)) attached to a hydroxyl group (\(\mathrm{-OH}\)). Carboxylic acids are widely recognized for their acidic properties, making them a vital component in both nature and industry.

• In water, they can donate a hydrogen ion (\(\mathrm{H}^+\)), leading to the formation of a carboxylate ion (\(\mathrm{COO}^-\)).
• This acidic characteristic is due to the resonance stabilization of the carboxylate ion.
• Carboxylic acids play crucial roles in biological systems, forming the backbone of amino acids.

Familiar examples include acetic acid, found in vinegar, and citric acid, commonly found in citrus fruits. These compounds add sour flavor and preservative properties in food applications.

Organic Chemistry

Organic chemistry focuses on the structure, properties, and reactions of organic compounds and materials. Typically, these compounds contain carbon atoms bonded to hydrogen, oxygen, and other elements. Carboxylic acids are a significant subset within this diverse branch. Organic chemistry is often concerned with understanding how organic molecules react and transform. Chemists study these transformations to develop new synthetic methods and to understand biological processes.

• The IUPAC nomenclature system is vital for naming these compounds systematically, ensuring each compound has a unique name.
• Structural knowledge is crucial for predicting chemical reactivity and mechanisms.
• Organic chemistry forms the basis of many industrial applications, from pharmaceuticals to polymers.

The ability to manipulate organic materials allows for tremendous scientific and economic progress.

Functional Groups

Functional groups are specific groupings of atoms within molecules that dictate their chemical reactions. These groups are the foundation of organic chemistry as they determine the characteristics and reactivities of molecules. The carboxyl group (\(\mathrm{COOH}\)) is an example of a functional group that imparts distinct properties to carboxylic acids.Some key features of functional groups include:

• Providing sites for chemical reactions, influencing both the physical and chemical properties of molecules.
• Functional groups allow chemists to predict reactivities in unknown compounds.
• They support the classification of compounds, such as alcohols, aldehydes, and acids.

Understanding functional groups is essential for mastering organic chemistry, as they enable the systematic categorization and prediction of behaviors for various organic compounds.