ChemistryChapter 8: Organic Chemistry
8.2.5 Naming Carboxylic Acids
**Carboxylic Acids:** Carboxylic acids are organic compounds characterized by the presence of the carboxyl group (-COOH)
Explanation level
Introduction
In the previous sections, we learned how to name alkanes, alkenes, alkynes, and alcohols. Now we turn to carboxylic acids, which contain a carboxyl group (-COOH) attached to a hydrocarbon chain.
The naming of carboxylic acids follows a similar pattern to alkanes, but with one important difference: the ending is "-oic acid" instead of "-ane". This tells us that the compound contains a carboxyl group.
This section explains how to name carboxylic acids using the stem and suffix system.
Definition
Carboxylic Acids: Carboxylic acids are organic compounds characterized by the presence of the carboxyl group (-COOH) attached to a hydrocarbon chain.
Naming Carboxylic Acids: This is shown by the ending "-oic acid" in their names. While naming carboxylic acids, the ending "e" of the name of the corresponding alkane containing the same number of carbon atoms is replaced by "oic acid".
In simple words: Carboxylic acids are hydrocarbons with a -COOH group, and their names end in -oic acid.
Main Idea
- Carboxylic acids contain the carboxyl group (-COOH) attached to a hydrocarbon chain.
- Their names end in "-oic acid".
- While naming carboxylic acids, the ending "e" of the name of the corresponding alkane is replaced by "oic acid".
- For example:
- One carbon alkane is methane → one carbon carboxylic acid is methanoic acid.
- Two carbon alkane is ethane → two carbon carboxylic acid is ethanoic acid.
- The position of the carboxyl carbon (C=O) is not mentioned in the name, because it is always numbered carbon 1. Numbering always starts from the carboxyl carbon atom in naming carboxylic acids.
Key point: Carboxylic acid names end in -oic acid, and the carboxyl carbon is always carbon 1.
Core Concept
| Feature | Description |
|---|---|
| Suffix | -oic acid |
| Functional group | Carboxyl group (-COOH) |
| General formula | CnH2n+1COOH |
| Naming rule | Replace the "e" of the corresponding alkane with "oic acid" |
| Position of carboxyl carbon | Always carbon 1 (not mentioned in the name) |
Key point: The suffix -oic acid tells you it is a carboxylic acid, and the carboxyl carbon is always carbon 1.
Detailed Explanation
What are Carboxylic Acids?
The carboxylic acids are characterized by the presence of the carboxyl group (-COOH) attached to a hydrocarbon chain.
This is shown by the ending "-oic acid" in their names.
While naming carboxylic acids, the ending "e" of the name of the corresponding alkane containing the same number of carbon atoms is replaced by "oic acid".
For example:
One carbon carboxylic acid:
H - C - OH (with a double bond to O)
Name: Methanoic acid Common name: Formic acid
Two carbon carboxylic acid:
CH3 - C - OH (with a double bond to O)
Name: Ethanoic acid Common name: Acetic acid
Key point: The name of a carboxylic acid is based on the corresponding alkane, with the "e" replaced by "oic acid".
The Position of the Carboxyl Carbon
The position of the carbonyl carbon (C=O) is not mentioned in the name, because it is always numbered carbon 1.
Numbering always starts from the carbonyl carbon atom in naming carboxylic acids.
Key point: The carboxyl carbon is always carbon 1, so its position is not mentioned in the name.
Examples of Carboxylic Acids
| Name | Molecular Formula | Condensed Formula | Common Name |
|---|---|---|---|
| Methanoic acid | HCOOH | HCOOH | Formic acid |
| Ethanoic acid | CH3COOH | CH3COOH | Acetic acid |
| Propanoic acid | C2H5COOH | CH3CH2COOH | Propionic acid |
| Butanoic acid | C3H7COOH | CH3CH2CH2COOH | Butyric acid |
Key point: The name of the carboxylic acid is determined by the number of carbon atoms in the chain.
Summary Table
| Stem | Number of C-atoms | Carboxylic Acid Name | Formula |
|---|---|---|---|
| Meth | 1 | Methanoic acid | HCOOH |
| Eth | 2 | Ethanoic acid | CH3COOH |
| Prop | 3 | Propanoic acid | CH3CH2COOH |
| But | 4 | Butanoic acid | CH3CH2CH2COOH |
| Pent | 5 | Pentanoic acid | CH3CH2CH2CH2COOH |
Intermediate Level
Naming carboxylic acids:
- Count the number of carbon atoms in the chain → choose the correct stem.
- Replace the "e" of the corresponding alkane with "oic acid".
- Write the full name (e.g., methanoic acid, ethanoic acid, propanoic acid, butanoic acid).
- The position of the carboxyl carbon is not mentioned because it is always carbon 1.
Examples:
| Formula | Name |
|---|---|
| HCOOH | Methanoic acid |
| CH3COOH | Ethanoic acid |
| CH3CH2COOH | Propanoic acid |
| CH3CH2CH2COOH | Butanoic acid |
Key point: The carboxyl carbon is always carbon 1, so its position is not mentioned in the name.
Solved Example
Example: Name the Following Carboxylic Acid
Question: Name the following carboxylic acid:
CH3 - CH2 - CH2 - C - OH (with a double bond to O on the C)
Solution:
Step 1: Count the number of carbon atoms in the chain.
- The chain has 4 carbon atoms → stem = but-
Step 2: Identify the suffix.
- The compound contains a -COOH group → suffix = -oic acid
Step 3: Write the name.
- Name: Butanoic acid
Final Answer: The name of the carboxylic acid is butanoic acid.
Concept Assessment Exercise 8.5
1. Write the name, displayed and structural formulae of a carboxylic acid containing 4-carbon atoms.
Answer:
- Name: Butanoic acid
- Condensed structural formula: CH3CH2CH2COOH
2. Identify the class of each of the following compounds from their names. Also, write their displayed structural formulas and condensed structural formulas: Pent-2-ol, Pentanoic acid, Pent-2-ene, Pentane.
Answer:
- Class: Alcohol
- Condensed formula: CH3 - CH(OH) - CH2 - CH2 - CH3
- Class: Carboxylic acid
- Condensed formula: CH3 - CH2 - CH2 - CH2 - COOH
- Class: Alkene
- Condensed formula: CH3 - CH = CH - CH2 - CH3
- Class: Alkane
- Condensed formula: CH3 - CH2 - CH2 - CH2 - CH3
Important Points
- - Carboxylic acids = organic compounds with a -COOH group attached to a hydrocarbon chain.
- - General formula: CnH2n+1COOH.
- - Names end in "-oic acid".
- - The name has two parts:
- 1. Stem — number of carbon atoms.
- 2. Suffix — -oic acid indicates a carboxylic acid.
- - The "e" of the corresponding alkane is replaced by "oic acid".
- - The position of the carboxyl carbon (C=O) is not mentioned because it is always carbon 1.
- - Examples:
- - Methanoic acid: HCOOH
- - Ethanoic acid: CH3COOH
- - Propanoic acid: CH3CH2COOH
- - Butanoic acid: CH3CH2CH2COOH
Remember
- - Carboxylic acids = hydrocarbons with a -COOH group.
- - Names end in -oic acid.
- - Stem tells the number of carbon atoms.
- - Replace the "e" of the alkane with "oic acid".
- - Carboxyl carbon is always carbon 1.
- - Position of carboxyl carbon is not mentioned.
- - Examples:
- - Methanoic acid: HCOOH
- - Ethanoic acid: CH3COOH
- - Propanoic acid: CH3CH2COOH
- - Butanoic acid: CH3CH2CH2COOH
Common Mistakes
| Mistake | Correction |
|---|---|
| Thinking carboxylic acid names end in -ol | Carboxylic acid names end in -oic acid |
| Forgetting the "e" is replaced by "oic acid" | The "e" of the corresponding alkane is replaced by "oic acid" |
| Indicating the position of the carboxyl carbon | The position is not mentioned because it is always carbon 1 |
| Confusing carboxylic acids with alcohols | Carboxylic acids: -oic acid; Alcohols: -ol |
| Forgetting the general formula of carboxylic acids | Carboxylic acids: CnH2n+1COOH |
| Thinking methanoic acid and ethanoic acid are the same | They have different numbers of carbon atoms |
| Forgetting the common names | Methanoic acid = formic acid; Ethanoic acid = acetic acid |
Quick Revision
Naming Carboxylic Acids:
The carboxylic acids are characterized by the presence of carboxylic group -COOH attached to a hydrocarbon chain. This is shown by ending -oic acid in their names. While naming carboxylic acids the ending "e" of the name of the corresponding alkane containing the same number of carbon atoms is replaced by 'oic acid'. For example;
- One carbon carboxylic acid:
- H - C - OH
- (with a double bond to O)
- Methanoic acid [Formic acid]
- Two carbon carboxylic acid:
- CH3 - C - OH
- (with a double bond to O)
- Ethanoic acid [Acetic acid]
Name shown in square brackets are common names of these compounds.
The position of carbonyl carbon (C=O) is not mentioned in the name, because it is always numbered carbon 1 i.e. numbering always starts from the carbonyl carbon atom in naming carboxylic acids.
Examples:
- Methanoic acid: HCOOH (Formic acid)
- Ethanoic acid: CH3COOH (Acetic acid)
- Propanoic acid: CH3CH2COOH
- Butanoic acid: CH3CH2CH2COOH
Concept Assessment Exercise 8.5:
- Write the name, displayed and structural formulae of a carboxylic acid containing 4-carbon atoms.
- Identify the class of each of the following compounds from their names. Also, write their displayed structural formulas and condensed structural formulas: Pent-2-ol, Pentanoic acid, Pent-2-ene, Pentane.
60-Second Revision
- Carboxylic acids = hydrocarbons with a -COOH group.
- Names end in -oic acid.
- Stem tells the number of carbon atoms.
- Replace the "e" of the alkane with "oic acid".
- Carboxyl carbon is always carbon 1.
- Position of carboxyl carbon is not mentioned.
- Examples:
- Methanoic acid: HCOOH (formic acid)
- Ethanoic acid: CH3COOH (acetic acid)
- Propanoic acid: CH3CH2COOH
- Butanoic acid: CH3CH2CH2COOH
- General formula: CnH2n+1COOH.
- ⚠️ Warning: the position of the carboxyl carbon is not mentioned in the name because it is always carbon 1.
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Sticky Notes · Quick Revision
Key Point 1
- Carboxylic acids = hydrocarbons with a -COOH group.
Key Point 2
- Names end in -oic acid.
Key Point 3
- Stem tells the number of carbon atoms.
Key Point 4
- Replace the "e" of the alkane with "oic acid".
Key Point 5
- Carboxyl carbon is always carbon 1.
Key Point 6
- Position of carboxyl carbon is not mentioned.
Key Point 7
- Examples:
Key Point 8
- Methanoic acid: HCOOH (formic acid)
Key Point 9
- Ethanoic acid: CH3COOH (acetic acid)
Key Point 10
- Propanoic acid: CH3CH2COOH
Key Point 11
- Butanoic acid: CH3CH2CH2COOH
Key Point 12
- General formula: CnH2n+1COOH.
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