ChemistryChapter 8: Organic Chemistry
8.2.4 Naming Alcohols
**Alcohols:** Alcohols are organic compounds characterized by the presence of the hydroxyl group (-OH)
Explanation level
Introduction
In the previous sections, we learned how to name alkanes, alkenes, and alkynes — hydrocarbons containing only carbon and hydrogen. Now we turn to alcohols, which contain a hydroxyl group (-OH) attached to a hydrocarbon chain.
The naming of alcohols follows a similar pattern to alkanes, but with one important difference: the ending is "-ol" instead of "-ane". This tells us that the compound contains a hydroxyl group.
This section explains how to name alcohols using the stem and suffix system, and how to indicate the position of the hydroxyl group.
Definition
Alcohols: Alcohols are organic compounds characterized by the presence of the hydroxyl group (-OH) attached to a hydrocarbon chain.
Naming Alcohols: This is shown by the ending "-ol" in their names. While naming alcohols, the "e" of the alkane containing the same number of carbon atoms is replaced by the suffix "-ol".
In simple words: Alcohols are hydrocarbons with an -OH group, and their names end in -ol.
Main Idea
- Alcohols contain the hydroxyl group (-OH) attached to a hydrocarbon chain.
- Their names end in "-ol".
- While naming alcohols, the "e" of the corresponding alkane is replaced by "-ol".
- For example:
- One carbon alkane is methane → one carbon alcohol is methanol.
- Two carbon alkane is ethane → two carbon alcohol is ethanol.
- Three carbon alkane is propane → three carbon alcohol is propanol.
- With larger chains, the position of the -OH group is indicated by a number in the name.
Key point: Alcohol names end in -ol, and the position of the -OH group is indicated by a number.
Core Concept
| Feature | Description |
|---|---|
| Suffix | -ol |
| Functional group | Hydroxyl group (-OH) |
| General formula | CnH2n+1OH |
| Naming rule | Replace the "e" of the corresponding alkane with "-ol" |
| Position of -OH group | Indicated by a number in the name |
Key point: The suffix -ol tells you it is an alcohol, and the number tells you where the -OH group is.
Detailed Explanation
What are Alcohols?
Alcohols are characterized by the presence of the hydroxyl group (-OH) attached to a hydrocarbon chain.
This is shown by the ending "-ol" in their names.
While naming alcohols, the "e" of the alkane containing the same number of carbon atoms is replaced by the suffix "-ol".
For example:
- One carbon alkane is methane → one carbon alcohol is methanol.
- Two carbon alkane is ethane → two carbon alcohol is ethanol.
Key point: The name of an alcohol is based on the corresponding alkane, with the "e" replaced by "-ol".
Naming Alcohols with Larger Chains
With larger chains, the position of the -OH group is indicated by a number in the name.
Numbering rule: Numbering is started from the end that gives the smaller number to the carbon atom bearing the -OH group.
Examples:
Propan-1-ol: The -OH group is attached to carbon 1.
CH3 - CH2 - CH2 - OH
Propan-2-ol: The -OH group is attached to carbon 2.
CH3 - CH(OH) - CH3
Butan-1-ol: The -OH group is attached to carbon 1.
CH3 - CH2 - CH2 - CH2 - OH
Butan-2-ol: The -OH group is attached to carbon 2.
CH3 - CH2 - CH(OH) - CH3
Key point: The position of the -OH group is indicated by a number in the name.
Examples of Alcohols
| Name | Molecular Formula | Condensed Formula |
|---|---|---|
| Methanol | CH3OH | CH3OH |
| Ethanol | C2H5OH | CH3CH2OH |
| Propan-1-ol | C3H7OH | CH3CH2CH2OH |
| Propan-2-ol | C3H7OH | CH3CH(OH)CH3 |
| Butan-1-ol | C4H9OH | CH3CH2CH2CH2OH |
| Butan-2-ol | C4H9OH | CH3CH2CH(OH)CH3 |
Key point: The name of the alcohol is determined by the number of carbon atoms and the position of the -OH group.
Summary Table
| Stem | Number of C-atoms | Alcohol Name (with -OH at position 1) |
|---|---|---|
| Meth | 1 | Methanol |
| Eth | 2 | Ethanol |
| Prop | 3 | Propan-1-ol |
| But | 4 | Butan-1-ol |
| Pent | 5 | Pentan-1-ol |
| Hex | 6 | Hexan-1-ol |
Intermediate Level
Naming alcohols:
- Count the number of carbon atoms in the chain → choose the correct stem.
- Replace the "e" of the corresponding alkane with -ol.
- Number the chain from the end nearest to the -OH group.
- Write the position of the -OH group as a number before the suffix.
- Write the full name (e.g., propan-1-ol, propan-2-ol).
Examples:
| Formula | Name |
|---|---|
| CH3OH | Methanol |
| CH3CH2OH | Ethanol |
| CH3CH2CH2OH | Propan-1-ol |
| CH3CH(OH)CH3 | Propan-2-ol |
| CH3CH2CH2CH2OH | Butan-1-ol |
| CH3CH2CH(OH)CH3 | Butan-2-ol |
Key point: The position of the -OH group is indicated by a number, and numbering starts from the end nearest to the -OH group.
Solved Example
Example: Name the Following Alcohol
Question: Name the following alcohol:
CH3 - CH2 - CH2 - CH2 - OH
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 an -OH group → suffix = -ol
Step 3: Determine the position of the -OH group.
- Number the chain from the end nearest to the -OH group.
- The -OH group is attached to carbon 1.
Step 4: Write the name.
- Name: Butan-1-ol
Final Answer: The name of the alcohol is butan-1-ol.
Concept Assessment Exercise 8.4
1. Write the name, display, and structural formula of an alcohol containing a 4-carbon chain with -OH group attached to a second carbon atom.
Answer:
- Name: Butan-2-ol
- Condensed structural formula: CH3 - CH2 - CH(OH) - CH3
2. Write the structural formulas of the following alcohols:
(a) Butan-1-ol
Answer:
- Condensed structural formula: CH3 - CH2 - CH2 - CH2 - OH
(b) Butan-2-ol
Answer:
- Condensed structural formula: CH3 - CH2 - CH(OH) - CH3
Hint from the source: Write a string of relevant numbers of carbon atoms and number them from one side. Attach the OH group on the indicated C-atom and then complete the structure by H-atoms.
Important Points
- - Alcohols = organic compounds with an -OH group attached to a hydrocarbon chain.
- - General formula: CnH2n+1OH.
- - Names end in "-ol".
- - The name has two parts:
- 1. Stem — number of carbon atoms.
- 2. Suffix — -ol indicates an alcohol.
- - The "e" of the corresponding alkane is replaced by "-ol".
- - For larger chains, the position of the -OH group is indicated by a number.
- - Numbering starts from the end nearest to the -OH group.
- - Examples:
- - Methanol: CH3OH
- - Ethanol: CH3CH2OH
- - Propan-1-ol: CH3CH2CH2OH
- - Propan-2-ol: CH3CH(OH)CH3
- - Butan-1-ol: CH3CH2CH2CH2OH
- - Butan-2-ol: CH3CH2CH(OH)CH3
Remember
- - Alcohols = hydrocarbons with an -OH group.
- - Names end in -ol.
- - Stem tells the number of carbon atoms.
- - Position of -OH group is indicated by a number.
- - Numbering starts from the end nearest to the -OH group.
- - Replace the "e" of the alkane with "-ol".
- - Examples:
- - Methanol: CH3OH
- - Ethanol: CH3CH2OH
- - Propan-1-ol: CH3CH2CH2OH
- - Propan-2-ol: CH3CH(OH)CH3
- - Butan-1-ol: CH3CH2CH2CH2OH
- - Butan-2-ol: CH3CH2CH(OH)CH3
Common Mistakes
| Mistake | Correction |
|---|---|
| Thinking alcohol names end in -ane | Alcohol names end in -ol |
| Forgetting to indicate the position of the -OH group | The position is indicated by a number in the name |
| Numbering from the wrong end | Numbering starts from the end nearest to the -OH group |
| Thinking the -OH group can be attached to any atom | The -OH group is attached to a carbon atom |
| Confusing alcohols with alkanes | Alcohols: -ol; Alkanes: -ane |
| Forgetting the general formula of alcohols | Alcohols: CnH2n+1OH |
| Thinking propan-1-ol and propan-2-ol are the same | They are isomers with different structures |
Quick Revision
Naming Alcohols:
Alcohols are characterized by the presence of the hydroxyl group (-OH) attached to a hydrocarbon chain. This is shown by the ending "ol" in their names. While naming alcohols the "e" of alkane containing the same number of carbon atoms is replaced by the suffix "ol". For example; one carbon alkane is methane, so the name of one carbon alcohol is methanol.
Examples:
- Methanol: CH3OH
- Ethanol: CH3CH2OH
- Propan-1-ol: CH3CH2CH2OH
- Propan-2-ol: CH3CH(OH)CH3
- Butan-1-ol: CH3CH2CH2CH2OH
- Butan-2-ol: CH3CH2CH(OH)CH3
Concept Assessment Exercise 8.4:
- Write the name, display and structural formula of an alcohol-containing 4-carbon chain with -OH group attached to a second carbon atom.
- Write the structural formulas of the following alcohols.
Hint: Write a string of relevant numbers of carbon atoms and number them from one side. Attach OH group on the indicated C-atom and then complete the structure by H-atoms.
60-Second Revision
- Alcohols = hydrocarbons with an -OH group.
- Names end in -ol.
- Stem tells the number of carbon atoms.
- Position of -OH group is indicated by a number.
- Numbering starts from the end nearest to the -OH group.
- Replace the "e" of the alkane with "-ol".
- Examples:
- Methanol: CH3OH
- Ethanol: CH3CH2OH
- Propan-1-ol: CH3CH2CH2OH
- Propan-2-ol: CH3CH(OH)CH3
- Butan-1-ol: CH3CH2CH2CH2OH
- Butan-2-ol: CH3CH2CH(OH)CH3
- General formula: CnH2n+1OH.
- ⚠️ Warning: numbering always starts from the end that gives the smaller number to the -OH group.
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Revision Zone
Review the key facts, formulas and checks before you move on.8.2.4 Naming Alcohols
Sticky Notes · Quick Revision
Key Point 1
- Alcohols = hydrocarbons with an -OH group.
Key Point 2
- Names end in -ol.
Key Point 3
- Stem tells the number of carbon atoms.
Key Point 4
- Position of -OH group is indicated by a number.
Key Point 5
- Numbering starts from the end nearest to the -OH group.
Key Point 6
- Replace the "e" of the alkane with "-ol".
Key Point 7
- Examples:
Key Point 8
- Methanol: CH3OH
Key Point 9
- Ethanol: CH3CH2OH
Key Point 10
- Propan-1-ol: CH3CH2CH2OH
Key Point 11
- Propan-2-ol: CH3CH(OH)CH3
Key Point 12
- Butan-1-ol: CH3CH2CH2CH2OH
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