1. Alcohols (R-OH)

Compounds formed by replacing a hydrogen atom of a hydrocarbon with an -OH group.

Preparation Methods

From Alkenes:
• Acid Catalyzed Hydration: Markovnikov addition.
• Hydroboration-Oxidation: Anti-Markovnikov addition (Yields 1° alcohols).
From Carbonyls:
• Reduction of Aldehydes (gives 1°) and Ketones (gives 2°) using LiAlH₄ or NaBH₄.
• Grignard Reagent: HCHO → 1°, Other Aldehydes → 2°, Ketones → 3°.

Chemical Properties & Distinction

Lucas Test (Distinction between 1°, 2°, 3°):

Reagent: Conc. HCl + Anhydrous ZnCl₂

3° Alcohol: Immediate turbidity (cloudiness).
2° Alcohol: Turbidity in 5 minutes.
1° Alcohol: No turbidity at room temperature.

2. Phenols (Ar-OH)

Preparation of Phenol

From Cumene (Commercial): Cumene →{O₂} Cumene hydroperoxide →{H^+} Phenol + Acetone.
From Benzene Sulphonic Acid: Fusion with NaOH at 573K.
From Diazonium Salts: Hydrolysis with warm water.

Chemical Reactions

1. Reimer-Tiemann Reaction:

Phenol + CHCl₃ + aq. NaOH → Salicylaldehyde.

2. Kolbe's Reaction:

Phenoxide ion + CO₂ &xrightarrow{H^+} Salicylic acid (Aspirin precursor).

Acidity of Phenol:

Phenols are more acidic than alcohols because the Phenoxide ion is resonance stabilized.
Effect of Substituents:
• Electron Withdrawing Groups (EWG like -NO₂) Increase acidity.
• Electron Donating Groups (EDG like -CH₃) Decrease acidity.

3. Ethers (R-O-R')

Preparation

Williamson Synthesis (S_N2):

Alkyl Halide + Sodium Alkoxide → Ether + NaX.
Note: Alkyl halide must be primary. If 3° halide is used, Elimination (alkene) occurs instead of substitution.

Chemical Properties

Cleavage by HI:

R-O-R' + HI → R-I + R'-OH (Lower alkyl group forms Iodide).
If one group is 3°, then 3° Iodide is formed (via S_N1).

4. Distinction Tests

Test	Alcohol	Phenol
FeCl₃ Test	No color	Violet coloration
Bromine Water	No reaction	White ppt (2,4,6-tribromophenol)
Iodoform Test	Ethanol/2-alcohols give yellow ppt	No reaction

5. Important Uses

Methanol: "Wood spirit", poisonous, used as solvent for paints.
Ethanol: In beverages, as an antiseptic, and fuel additive (Gasohol).
Phenol: Production of Bakelite (plastic) and Aspirin.
Diethyl Ether: Formerly used as an anesthetic, common lab solvent.

Numericals & HOTS

Q1. Identification by Lucas Test

An organic compound A (C₄H₁₀O) does not react with Lucas reagent at room temperature but gives a positive Iodoform test. On heating with conc. H₂SO₄ at 443 K, it forms compound B. Identify A and B.

Solution:
1. Formula C₄H₁₀O: Possible isomers: Butan-1-ol, Butan-2-ol, 2-Methylpropan-1-ol, 2-Methylpropan-2-ol.
2. Lucas Test: No reaction at room temperature usually implies it is a 1° alcohol. However, 1° alcohols do not give the Iodoform test.
3. Iodoform Test: Requires a CH₃CH(OH)- group. The only 4-carbon alcohol with this group is Butan-2-ol.
4. Result: A is Butan-2-ol (Note: It reacts with Lucas reagent in 5 mins, not immediately). B is But-2-ene (major product formed by dehydration).

Q2. Williamson Synthesis Logic

To prepare tert-butyl ethyl ether, which set of reagents is preferred?
(i) CH₃CH₂ONa + (CH₃)₃C-Cl
(ii) (CH₃)₃CONa + CH₃CH₂-Cl

Solution:
Set (ii) is correct.

Williamson synthesis is an S_N2 reaction. In set (i), the halide is 3° (tertiary). Alkoxides are strong bases; with 3° halides, elimination occurs to give 2-methylpropene. In set (ii), the halide is 1° (primary), favoring substitution to form the ether.

Q3. Cleavage with HI

Predict the products when Anisole (Methoxybenzene) reacts with HI at 373 K.

Solution:
Products: Phenol (C₆H₅OH) and Methyl Iodide (CH₃I).

Reason: The bond between Oxygen and the Phenyl ring has partial double bond character due to resonance. It is much stronger than the O-Methyl bond. Thus, the iodide ion attacks the methyl group, leaving the phenol intact.

Q4. Substituent Effects

Arrange in increasing order of acidity: p-Nitrophenol, m-Nitrophenol, Phenol, p-Cresol.

Solution:
1. Nitro group (-NO₂): EWG, increases acidity. Para is more acidic than meta due to resonance.
2. Methyl group (-CH₃): EDG, decreases acidity.

Order: p-Cresol < Phenol < m-Nitrophenol < p-Nitrophenol

Q5. Rearrangement

Major product of dehydration of 3,3-Dimethylbutan-2-ol?

Solution:
1. Protonation and loss of water forms a 2° carbocation.
2. 1,2-Methyl shift occurs to form a more stable 3° carbocation.
3. Elimination of H⁺ gives the stable alkene.
Product: 2,3-Dimethylbut-2-ene

Q6. Mass Calculation

Mass of Salicylic acid (M.M. 138) to produce 10 g of Aspirin (M.M. 180)?

Solution:
Salicylic acid + Acetic Anhydride → Aspirin.
138 g of acid gives 180 g of Aspirin.
For 10 g Aspirin: (138 / 180) * 10 = 7.67 g.

Q7. Phenol Bromination

Why does Phenol + Br₂/H₂O give 2,4,6-tribromophenol?

Solution:
In polar water, phenol ionizes into phenoxide ion. The oxygen's negative charge activates the ring extensively. In non-polar CS₂, ionization is low, resulting only in mono-substitution.

Q8. Reagent Prediction

Distinguish between Propan-1-ol and Propan-2-ol.

Solution:
Iodoform Test: Propan-2-ol (a 2° alcohol with CH₃CH(OH)- group) gives a yellow precipitate of CHI₃. Propan-1-ol does not.

Q9. Markovnikov vs Anti-M

Product of Propene + (i) B₂H₆ (ii) H₂O₂/OH^-?

Solution:
This is Hydroboration-Oxidation. It results in Anti-Markovnikov addition of water.
Product: Propan-1-ol.

Q10. Phenol vs Alcohol

Why is Phenol more acidic than Ethanol?

Solution:
In phenol, the phenoxide ion is stabilized by resonance. In ethanol, the ethoxide ion has no resonance and is destabilized by the +I effect of the ethyl group.

Important Reactions

1. Alcohol Preparation Trends

Hydroboration-Oxidation:

Alkene + (BH₃)₂ / H₂O₂, OH^- → 1° Alcohol

(Anti-Markovnikov Hydration; No rearrangement)

Grignard + Carbonyl:

HCHO + RMgX → 1° Alcohol
RCHO + RMgX → 2° Alcohol
R₂CO + RMgX → 3° Alcohol

2. Phenol Name Reactions

Reimer-Tiemann Reaction:

Phenol + CHCl₃ + NaOH → Salicylaldehyde

[Image of Reimer-Tiemann reaction mechanism]

Kolbe’s Reaction:

Phenoxide + CO₂ &xrightarrow{H^+} Salicylic Acid

3. Ether Cleavage with HI

Case 1: 1° or 2° alkyl groups (S_N2):

R-O-R' + HI → Smaller R-I + Larger R'-OH

Case 2: One 3° alkyl group (S_N1):

(CH₃)₃C-O-CH₃ + HI → (CH₃)₃C-I + CH₃OH

20 Golden Facts (NEET)

1. Boiling Point: Alcohols and phenols have much higher boiling points than ethers or hydrocarbons of comparable mass due to Intermolecular Hydrogen Bonding.
2. Solubility: Lower alcohols are miscible with water in all proportions due to H-bonding, but solubility decreases as the size of the alkyl (hydrophobic) group increases.
3. Acidity Order: Water > 1° Alcohol > 2° Alcohol > 3° Alcohol. (Alcohols are even weaker acids than water, except Methanol).
4. Phenol Acidity: Phenol is more acidic than alcohols because the phenoxide ion is resonance-stabilized, whereas the alkoxide ion is not.
5. Picric Acid: 2,4,6-Trinitrophenol is called Picric Acid. It is very acidic due to the presence of three electron-withdrawing nitro (-NO₂) groups.
6. Oxidation: 1° alcohols → Aldehydes → Acids; 2° alcohols → Ketones; 3° alcohols are resistant to oxidation but undergo dehydration under drastic conditions.
7. PCC Reagent: Pyridinium Chlorochromate (PCC) is the best reagent to oxidize 1° alcohols to Aldehydes without further oxidation to carboxylic acids.
8. Victor Meyer Test: Red colour = 1° alcohol; Blue colour = 2° alcohol; Colourless = 3° alcohol. (RBC rule).
9. Lucas Reagent: A mixture of conc. HCl and ZnCl₂. It distinguishes alcohols based on the rate of formation of alkyl chlorides (turbidity).
10. Dehydration of Ethanol: At 443 K (conc. H₂SO₄) → Ethene. At 413 K → Ethoxyethane (Ether).
11. Electrophilic Substitution: The -OH group in phenol is ortho and para directing and highly activating due to resonance.
12. Bromine Water/Phenol: Reaction of phenol with bromine water gives a white precipitate of 2,4,6-tribromophenol.
13. Aspirin Synthesis: Acetylation of salicylic acid with acetic anhydride in the presence of acid gives Acetylsalicylic acid (Aspirin).
14. Williamson Synthesis: It involves an S_N2 attack of an alkoxide ion on a primary alkyl halide. 3° halides give alkenes.
15. Ethers as Lewis Bases: Ethers can donate lone pairs of electrons to Lewis acids like BF₃ to form coordination complexes called etherates.
16. Peroxide Formation: Ethers on long exposure to air and light form highly explosive peroxides.
17. Denatured Alcohol: Ethyl alcohol made unfit for drinking by adding Methanol, Pyridine, or Copper Sulphate.
18. Dow's Process: Industrial preparation of phenol from Chlorobenzene using NaOH at high temperature (623 K) and pressure (300 atm).
19. Power Alcohol: A mixture of 20% Ethanol and 80% Petrol used as fuel in internal combustion engines.
20. Catalyst in Williamson: If we want to prepare tert-butyl methyl ether, we must use Sodium tert-butoxide and Methyl bromide, NOT Sodium methoxide and tert-butyl bromide.

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