Problem 47 - Chemistry: The Central Science in SI Units, Global Edition

Question

The IUPAC name for a carboxylic acid is based on the name of the hydrocarbon with the same number of carbon atoms. The ending -oic is appended, as in ethanoic acid, which is the IUPAC name for acetic acid. Draw the structure of the following acids: (a) methanoic acid, \((\mathbf{b})\) pentanoic acid, \((\mathbf{c}) 2\) -chloro-3-methyldecanoic acid.

Step-by-Step Solution

Answer

The structures of the carboxylic acids are as follows: (a) Methanoic Acid: HCOOH, (b) Pentanoic Acid: CH₃CH₂CH₂CH₂COOH, and (c) 2-Chloro-3-Methyldecanoic Acid: CH₃(CH₂)₇COOH | CH₃ | Cl

Step 1: (a) Methanoic Acid

To draw the structure of methanoic acid, we first need to find the number of carbon atoms. Since the prefix "meth" corresponds to one carbon atom, and it's a carboxylic acid, we know there must be a COOH group attached to it. The structure of methanoic acid will therefore be: HCOOH

Step 2: (b) Pentanoic Acid

To draw the structure of pentanoic acid, we first need to find the number of carbon atoms. The prefix "pent" corresponds to five carbon atoms. As it's a carboxylic acid, we will have a COOH group attached to one end of the carbon chain. The structure of pentanoic acid will therefore be: CH₃CH₂CH₂CH₂COOH

Step 3: (c) 2-Chloro-3-Methyldecanoic Acid

To draw the structure of 2-chloro-3-methyldecanoic acid, we need to: 1. Identify the number of carbon atoms: The prefix "decan" corresponds to 10 carbon atoms. 2. Identify the substituents: At the 2nd carbon atom, there is a chlorine atom (2-chloro). At the 3rd carbon atom, there is a methyl group (3-methyl). Once we have identified the substituents and the number of carbon atoms, we can draw the structure: CH₃(CH₂)₇COOH | CH₃ | Cl

Key Concepts

IUPAC nomenclature

IUPAC nomenclature is a systematic method of naming chemical compounds according to specific rules set by the International Union of Pure and Applied Chemistry (IUPAC). It provides a way to ensure that each chemical name conveys unique and meaningful information about the structure of a compound. For carboxylic acids, the IUPAC naming involves reading the name of the parent hydrocarbon chain, followed by replacing the suffix with '-oic acid' to indicate the presence of the carboxyl group, COOH.
For example:

• Methanoic acid is the smallest carboxylic acid, indicated by the prefix 'meth-', meaning it has one carbon atom.
• Pentanoic acid uses 'pent-', meaning it has a five-carbon chain.
• 2-Chloro-3-methyldecanoic acid includes the 'decan-' prefix for a ten-carbon chain with additional instructions for chlorine and methyl group positions.

By specifying positions for substituents and chain lengths precisely, IUPAC nomenclature helps chemists easily communicate complex organic structures.

Carboxylic acids

Carboxylic acids are a fundamental group in organic chemistry, characterized by their functional group \(\text{-COOH}\). This functional group comprises a carbonyl group (C=O) attached to a hydroxyl group (OH). The properties of carboxylic acids are largely due to this unique arrangement, which can participate in hydrogen bonding.
Carboxylic acids are known for various chemical reactions, including esterification, where they react with alcohols to form esters. They are also notable for their ability to donate protons (H⁺ ions), thus acting as weak acids. Functional groups directly impact their reactivity and how they interact in formulation and synthesis. The naming (such as methanoic, pentanoic, and decanoic acids) highlights the length of the carbon chain and any substituents that might modify their behavior and use in industrial applications.

Chemical structure drawing

Chemical structure drawing is a crucial practice in organic chemistry that visually represents the arrangement of atoms within a molecule. It ensures clarity and precision by showing exactly how atoms are bonded in a chemical compound. For carboxylic acids, it means illustrating the backbone of carbon atoms along with the \(\text{-COOH}\) group.
When drawing structures:

• Start by sketching the carbon chain according to the number indicated by the name (e.g., one carbon for methanoic acid, five for pentanoic acid).
• Add functional groups like the carboxyl group \(\text{-COOH}\).
• Positional isomers, such as those found in 2-chloro-3-methyldecanoic acid, include specific attachments at designated carbon atoms.

Through drawing, chemists can better predict properties and reactions of the compounds, facilitating their understanding and communication within the scientific community.