Alcohol
A concise revision guide to the alcohol functional group, the hydroxyl group, the -ol suffix, naming diols and triols, and the priority of the -OH group in organic nomenclature.
What Is an Alcohol?
An alcohol is an organic compound containing the hydroxyl functional group, written as -OH.
The oxygen atom in the -OH group is bonded to a carbon atom in the organic molecule. This functional group determines the characteristic chemistry of alcohols.
In naming, the -OH group is usually shown using the suffix -ol.
Key idea: The alcohol functional group is the hydroxyl group, -OH. Do not confuse this with the hydroxide ion, OH–.
The hydroxyl group is the identifying functional group of alcohols and is written as -OH in organic formulae.
Naming Alcohols Using the -ol Suffix
Alcohols are named using the suffix -ol.
If the position of the -OH group needs to be shown, the position number is placed between the name stem and the -ol suffix.
For example, propan-1-ol has a three-carbon chain and the -OH group is attached to carbon 1.
| Homologous series | Functional group | Prefix | Suffix | Example |
|---|---|---|---|---|
| Alcohols | -OH | hydroxy- | -ol | propan-1-ol |
The number 1 shows that the -OH group is bonded to the first carbon atom in the propyl chain.
Alcohols with Two or More -OH Groups
If a molecule contains two or more -OH groups, prefixes such as di- and tri- are used.
In these cases, the final e in the alkane stem is retained before the suffix. For example, ethane becomes ethane-1,2-diol, not ethan-1,2-diol.
Two -OH groups
Use -diol, with numbers showing the positions of both -OH groups.
Three -OH groups
Use -triol, with numbers showing the positions of all three -OH groups.
Ethane-1,2-diol contains two -OH groups, so the diol suffix is used and the e in ethane is retained.
Propane-1,2,3-triol contains three -OH groups, so each position is included before the triol suffix.
Priority of the -OH Group
The -OH group has higher priority than both halogenoalkanes and alkenes when naming organic molecules.
This means the carbon chain is numbered so that the -OH group is on the lowest possible carbon, often carbon 1.
If a molecule also contains a C=C double bond or halogen substituents, these are still included in the name, but the -OH group controls the main suffix and the numbering direction.
Exam focus: When several groups are present, first identify the highest-priority group that will control the suffix and numbering.
The -ol suffix and carbon 1 position are used because the -OH group has higher naming priority than the C=C bond and chloro substituents.
When Alcohol Is Named as Hydroxy-
If a compound contains an -OH group and another functional group with higher priority, the higher-priority group takes the suffix form.
In that situation, the -OH group is named using the prefix hydroxy-.
This is why it is important to recognise whether -OH is acting as the main functional group or as a substituent in the name.
| Naming situation | How -OH appears in the name | Example naming logic |
|---|---|---|
| -OH is the main functional group | Use the suffix -ol | propan-1-ol |
| A higher-priority group controls the suffix | Use the prefix hydroxy- | The higher-priority group takes the suffix form |
Remember: The usual alcohol naming pattern is -ol, but hydroxy- is used when the -OH group is not the highest-priority group.
Check Your Understanding
Use these short activities to check alcohol functional groups, -ol naming, diols, triols and functional group priority before moving on.
Master Topic 6A/6B Organic Chemistry and Alkanes for Edexcel A Level Chemistry
Continue from these free revision notes into the full Topic 6A/6B Organic Chemistry and Alkanes course for Edexcel A Level Chemistry Paper 2 (9CH0/02), with guided video teaching, diagnostic MCQ practice, teacher-marked short-answer questions and a specification assignment with a personalised progress report.
Guided video teaching
Learn the chemistry and exam technique through structured video lessons with worked examples and walkthroughs.
Instant MCQ feedback
Auto-marked MCQ quizzes provide immediate diagnostic feedback for every answer choice.
Teacher-marked SAQs
Submit written exam responses and receive chemistry specialist feedback with improvement guidance.
Progress tracking
Identify strengths and weaknesses across the full Topic 6A/6B specification with targeted reporting.
See how the course works
Click play to start the course preview animation.
Some ionic radii are shown.
| Ion | Ionic radius / nm |
|---|---|
| Na+ | 0.102 |
| K+ | 0.138 |
| F− | 0.133 |
| Cl− | 0.180 |
Which compound has the strongest ionic bonding?
Explain why the metallic bonding in magnesium is much stronger than that in sodium.
Copyright notice: This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.