1. Introduction to Alcohols

Examples:

2. Classification of Alcohols

2.1 Based on Number of –OH Groups

2.2 Primary, Secondary and Tertiary Monohydric Alcohols

The classification depends on how many carbon atoms are directly attached to the carbon bearing –OH.

3. Nomenclature and Isomerism

3.1 IUPAC Nomenclature

1. Select the longest carbon chain containing the carbon bearing –OH.
2. Replace the terminal “e” of the parent alkane with “ol”.
3. Number the chain so the –OH group receives the lowest possible locant.
4. Indicate substituents with their positions.

3.2 Isomerism

Monohydric alcohols may show:

• chain isomerism — different carbon skeleton;
• position isomerism — different position of –OH;
• functional isomerism with ethers for suitable molecular formulae;
• optical isomerism where a chiral carbon is present.

4. Distinction of 1°, 2° and 3° Alcohols by Victor Meyer’s Method

Victor Meyer’s method distinguishes primary, secondary and tertiary alcohols through conversion to characteristic nitro compounds followed by treatment with nitrous acid and alkali.

General Steps

1. Convert the alcohol into the corresponding alkyl iodide.
2. Convert the alkyl iodide into a nitroalkane using silver nitrite.
3. Treat the product with nitrous acid.
4. Add alkali and observe the colour.

5. Preparation of Monohydric Alcohols

5.1 From Haloalkanes

Aqueous hydroxide replaces halogen by –OH:

Example

5.2 From Primary Amines

Primary aliphatic amines react with nitrous acid to give alcohols with evolution of nitrogen gas.

Example

5.3 From Esters

Hydrolysis of an ester produces an alcohol and a carboxylic acid (or carboxylate in alkaline hydrolysis).

6. Industrial Preparation of Alcohols

6.1 Oxo Process

In the oxo process (hydroformylation), an alkene reacts with carbon monoxide and hydrogen to form an aldehyde. The aldehyde is then hydrogenated to an alcohol containing one more carbon atom than the starting alkene.

6.2 Hydroboration–Oxidation

Hydroboration followed by oxidation converts an alkene into an alcohol. The net addition places –OH at the less substituted carbon in the usual anti-Markovnikov orientation.

6.3 Fermentation of Sugar

Yeast enzymes convert fermentable sugars into ethanol and carbon dioxide under suitable anaerobic conditions.

The process typically requires an aqueous sugar solution, yeast and controlled temperature. Industrial ethanol is separated and concentrated after fermentation.

7. Common Terms Related to Ethanol

8. Physical Properties of Monohydric Alcohols

Alcohols contain a polar O–H bond and can form intermolecular hydrogen bonds. This strongly affects boiling point and water solubility.

9. Chemical Properties: Replacement of –OH by Halogen

9.1 Reaction with Hydrogen Halides

Example

9.2 With Phosphorus Trihalides

9.3 With Phosphorus Pentachloride

9.4 With Thionyl Chloride

10. Action with Reactive Metals

Alcohols react with strongly electropositive metals such as sodium, potassium and lithium to form alkoxides and hydrogen gas.

Example

11. Dehydration of Alcohols

11.1 Ethanol to Ethene

11.2 Orientation in Unsymmetrical Alcohols

Where more than one alkene can form, the more substituted alkene is commonly the major product under ordinary Saytzeff-type conditions.

12. Oxidation of Primary, Secondary and Tertiary Alcohols

Acidified potassium dichromate or potassium permanganate can oxidize alcohols. The products depend strongly on whether the alcohol is primary, secondary or tertiary.

12.1 Primary Alcohol

Thus a primary alcohol first gives an aldehyde and, under stronger/prolonged oxidation, a carboxylic acid.

12.2 Secondary Alcohol

A secondary alcohol gives a ketone.

12.3 Tertiary Alcohol

Tertiary alcohols do not have a hydrogen on the carbon bearing –OH. They therefore resist mild oxidation that leaves the carbon skeleton intact. Strong conditions can cause carbon–carbon bond cleavage, but that is beyond the simple school-level oxidation pattern.

13. Catalytic Dehydrogenation and Dehydration

When alcohol vapour is passed over heated copper, primary and secondary alcohols undergo dehydrogenation, while tertiary alcohols preferentially dehydrate because no suitable α-hydrogen is available for the same dehydrogenation pattern.

13.1 Primary Alcohol

13.2 Secondary Alcohol

13.3 Tertiary Alcohol

14. Esterification Reaction

Example: Ethyl Ethanoate

15. Test of Ethanol

15.1 Iodoform Test

Ethanol gives a positive iodoform test with iodine in alkaline solution. A yellow precipitate of iodoform, CHI₃, is formed.

A commonly written overall equation is:

16. High-Yield Reaction Summary

17. Common Exam Mistakes

18. Worked Examples

19. Important Exam Questions

Short-Answer Questions

1. Define alcohol and monohydric alcohol.
2. Classify monohydric alcohols as primary, secondary and tertiary with examples.
3. Give IUPAC names of CH₃CH₂OH, CH₃CHOHCH₃ and (CH₃)₃COH.
4. What kinds of isomerism are shown by monohydric alcohols?
5. State the observations for 1°, 2° and 3° alcohols in Victor Meyer’s method.
6. How is ethanol prepared from bromoethane?
7. How is an alcohol formed from a primary amine?
8. How does ester hydrolysis produce an alcohol?
9. What is the oxo process?
10. What is hydroboration–oxidation?
11. Write the fermentation equation for glucose.
12. Define absolute alcohol and rectified spirit.
13. What is denatured alcohol?
14. Why do alcohols have comparatively high boiling points?
15. Why does solubility of alcohols in water decrease with increasing alkyl-chain length?
16. Write the reaction of ethanol with sodium.
17. What is dehydration of alcohol?
18. State the oxidation products of 1°, 2° and 3° alcohols.
19. What is catalytic dehydrogenation?
20. Define esterification with an example.
21. Describe the iodoform test of ethanol.

Long-Answer Questions

1. Explain nomenclature, classification and isomerism of monohydric alcohols.
2. Describe Victor Meyer’s method for distinguishing primary, secondary and tertiary alcohols.
3. Describe preparation of monohydric alcohols from haloalkanes, primary amines and esters.
4. Explain industrial preparation of alcohol by oxo process, hydroboration–oxidation and fermentation.
5. Explain the common terms absolute alcohol, power alcohol, denatured alcohol, rectified spirit and alcoholic beverage.
6. Explain physical properties of alcohols on the basis of hydrogen bonding.
7. Describe reactions of alcohols with HX, PCl₃, PCl₅ and SOCl₂.
8. Explain dehydration of alcohols with a suitable example.
9. Compare oxidation of primary, secondary and tertiary alcohols.
10. Explain catalytic dehydrogenation of primary and secondary alcohols and dehydration of tertiary alcohols.
11. Explain esterification with an example.
12. Describe the iodoform test of ethanol, including observation and equation.

Conversion Questions

1. Bromoethane → ethanol.
2. Ethylamine → ethanol.
3. Ethanol → bromoethane.
4. Ethanol → chloroethane using SOCl₂.
5. Ethanol → sodium ethoxide.
6. Ethanol → ethene.
7. Ethanol → ethanal → ethanoic acid.
8. Propan-2-ol → propanone.
9. Ethanol + ethanoic acid → ethyl ethanoate.
10. Glucose → ethanol.

Diagram Questions

1. Draw the classification of 1°, 2° and 3° alcohols.
2. Draw the Victor Meyer test flowchart.
3. Draw a preparation map from haloalkane, primary amine and ester.
4. Draw the oxo-process flow diagram.
5. Draw hydroboration–oxidation of ethene.
6. Draw the fermentation process.
7. Draw intermolecular hydrogen bonding between alcohol molecules.
8. Draw the oxidation map of 1°, 2° and 3° alcohols.
9. Draw the catalytic behaviour of alcohols over heated copper.
10. Draw the iodoform test observation for ethanol.

20. One-Minute Revision

• Alcohols have –OH bonded to an sp³ carbon; general form R–OH.
• Monohydric alcohols contain one –OH group.
• 1°, 2° and 3° classification depends on the carbon bearing –OH.
• Victor Meyer: primary gives red, secondary gives blue, tertiary gives no characteristic red/blue colour.
• Haloalkane + aqueous KOH gives alcohol.
• Primary amine + HNO₂ gives alcohol + N₂.
• Ester hydrolysis can produce an alcohol.
• Oxo process: alkene → aldehyde → alcohol.
• Hydroboration–oxidation converts alkene to alcohol.
• Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
• Absolute alcohol is nearly water-free; rectified spirit is concentrated ethanol–water mixture.
• Alcohols hydrogen-bond, giving relatively high boiling points.
• 2ROH + 2Na → 2RONa + H₂.
• Dehydration gives an alkene + water.
• 1° oxidation: aldehyde then acid.
• 2° oxidation: ketone.
• 3° alcohols resist mild oxidation.
• Heated Cu: 1° → aldehyde + H₂; 2° → ketone + H₂.
• Esterification: alcohol + carboxylic acid ⇌ ester + water.
• Ethanol gives yellow CHI₃ in the iodoform test.

21. Diagram Practice

Students should practice these diagrams for the NEB examination:

1. Classification of primary, secondary and tertiary alcohols.
2. Victor Meyer’s method flowchart.
3. Preparation of alcohol from haloalkane, amine and ester.
4. Oxo-process flow diagram.
5. Hydroboration–oxidation of ethene.
6. Fermentation of glucose to ethanol.
7. Hydrogen bonding between alcohol molecules.
8. Dehydration of alcohol to alkene.
9. Oxidation map of 1°, 2° and 3° alcohols.
10. Catalytic dehydrogenation/dehydration pattern.
11. Iodoform test of ethanol.