NCERT Solutions

1. 2,2,4-Trimethylpentan-3-ol
2. 5-Ethylheptane-2,4-diol
3. Butane-1,3-diol
4. Propane-1,2,3-triol (Glycerol)
5. 2-Methylphenol (o-Cresol)
6. 4-Methylphenol (p-Cresol)
7. 2,5-Dimethylphenol
8. 2,6-Dimethylphenol
9. 1-Methoxy-2-methylpropane
10. Ethoxybenzene (Phenetole)
11. 1-Phenoxyheptane
12. 2-Methoxypropane

• Pentan-1-ol: \(CH_3(CH_2)_3CH_2OH\) (Primary)
• Pentan-2-ol: \(CH_3(CH_2)_2CH(OH)CH_3\) (Secondary)
• Pentan-3-ol: \(CH_3CH_2CH(OH)CH_2CH_3\) (Secondary)
• 3-Methylbutan-1-ol: \((CH_3)_2CHCH_2CH_2OH\) (Primary)
• 2-Methylbutan-1-ol: \(CH_3CH_2CH(CH_3)CH_2OH\) (Primary)
• 3-Methylbutan-2-ol: \((CH_3)_2CHCH(OH)CH_3\) (Secondary)
• 2-Methylbutan-2-ol: \((CH_3)_2C(OH)CH_2CH_3\) (Tertiary)
• 2,2-Dimethylpropan-1-ol: \((CH_3)_3CCH_2OH\) (Primary)

Propanol (\(C_3H_7OH\)) molecules are associated via strong intermolecular hydrogen bonding due to the polar -OH group. Butane (\(C_4H_{10}\)) is a non-polar hydrocarbon where molecules are held together by weak Van der Waals forces (London dispersion forces). Since hydrogen bonds require much more energy to break than Van der Waals forces, propanol has a significantly higher boiling point.

Solubility in water depends on the ability to form hydrogen bonds with water molecules. Alcohols possess a polar -OH group that can form hydrogen bonds with water, making them soluble. Hydrocarbons are non-polar and hydrophobic; they cannot form hydrogen bonds with water, hence they are insoluble.

It is a method to convert alkenes into alcohols. It involves the addition of diborane (\(B_2H_6\)) to an alkene to form trialkylborane, which is then oxidized by alkaline hydrogen peroxide to alcohol. The net result is the addition of water according to Anti-Markovnikov’s rule.

There are three isomers known as Cresols:

1. 2-Methylphenol (o-Cresol): Benzene with -OH at C1, -CH3 at C2.
2. 3-Methylphenol (m-Cresol): Benzene with -OH at C1, -CH3 at C3.
3. 4-Methylphenol (p-Cresol): Benzene with -OH at C1, -CH3 at C4.

o-Nitrophenol is steam volatile.

Reason: o-Nitrophenol forms Intramolecular Hydrogen Bonds (within the molecule), which prevents the association of molecules. This lowers its boiling point. In contrast, p-Nitrophenol forms Intermolecular Hydrogen Bonds (between different molecules), causing association and a higher boiling point, making it non-volatile.

Dow’s Process:

Attack of \(H_3O^+\) on ethene to form ethyl carbocation.
\(CH_2=CH_2 + H^+ \rightleftharpoons CH_3-CH_2^+\)

Water attacks the carbocation.
\(CH_3-CH_2^+ + H_2O \to CH_3-CH_2-OH_2^+\)

Loss of proton to form ethanol.
\(CH_3-CH_2-OH_2^+ \rightleftharpoons CH_3CH_2OH + H^+\)

• (i): Acid catalysed hydration of Styrene (\(C_6H_5CH=CH_2\)).
• (ii): Hydrolysis of Chloromethylcyclohexane (\(C_6H_{11}CH_2Cl\)) with aqueous NaOH (\(S_N2\)).
• (iii): Hydrolysis of 1-Chloropentane with aqueous NaOH (\(S_N2\)).

1. With Na: \(2C_6H_5OH + 2Na \to 2C_6H_5ONa + H_2\).
2. With NaOH: \(C_6H_5OH + NaOH \to C_6H_5ONa + H_2O\).

Phenol is more acidic than ethanol because the phenoxide ion formed is stabilized by resonance. The ethoxide ion is destabilized by the +I effect of the ethyl group.

• Nitro group (\(-NO_2\)): Is an electron-withdrawing group (-I, -R). It withdraws electron density, weakening the O-H bond and stabilizing the phenoxide ion via resonance. This increases acidity.
• Methoxy group (\(-OCH_3\)): Is an electron-donating group (+R). It increases electron density on the ring, destabilizing the phenoxide ion. This decreases acidity.

The -OH group has lone pairs on oxygen. It donates electrons to the benzene ring via the Resonance (+R) effect. This increases the electron density in the ring, particularly at the ortho and para positions. Therefore, electrophiles attack these electron-rich positions more readily than in benzene.

• (i) Kolbe’s Reaction: Phenol treated with NaOH forms phenoxide, which reacts with \(CO_2\) followed by acidification to give Salicylic Acid (2-Hydroxybenzoic acid).
• (ii) Reimer-Tiemann: Phenol treated with \(CHCl_3\) and aq. NaOH introduces a -CHO group at ortho position, forming Salicylaldehyde.
• (iii) Williamson Synthesis: Reaction of alkyl halide with sodium alkoxide to form ether (\(R-X + R’ONa \to R-O-R’\)). Best with primary halides.
• (iv) Unsymmetrical Ether: Ethers where the two groups attached to oxygen are different (e.g., Ethyl methyl ether).

\(CH_3CH_2OH + H^+ \rightleftharpoons CH_3CH_2OH_2^+\) (Ethyloxonium ion).

\(CH_3CH_2OH_2^+ \to CH_3C^+H_2 + H_2O\). (Slow, Rate determining).

\(H-CH_2-C^+H_2 \to CH_2=CH_2 + H^+\).

• (i) Oxidation of 1° alcohol to carboxylic acid: Acidified \(KMnO_4\).
• (ii) Oxidation of 1° alcohol to aldehyde: PCC (Pyridinium chlorochromate).
• (iii) Bromination of phenol to 2,4,6-tribromophenol: Bromine water.
• (iv) Benzyl alcohol to benzoic acid: Acidified \(KMnO_4\).
• (v) Dehydration of propan-2-ol to propene: Conc. \(H_2SO_4\) at 443 K.
• (vi) Butan-2-one to butan-2-ol: \(NaBH_4\) or \(LiAlH_4\).

Ethanol contains a polar -OH group allowing it to form intermolecular hydrogen bonds. Methoxymethane (an ether) lacks hydrogen attached to oxygen and cannot form hydrogen bonds. Hydrogen bonding is stronger than dipole-dipole attraction, resulting in a higher boiling point for ethanol.

• (i) \(CH_3OCH_2CH(CH_3)_2\): 1-Methoxy-2-methylpropane.
• (ii) \(C_6H_5OCH_2CH_3\): Ethoxybenzene.
• (iii) \(C_6H_5O(CH_2)_6CH_3\): 1-Phenoxyheptane.
• (iv) \(CH_3OCH_2CH_2OCH_3\): 1,2-Dimethoxyethane.

Williamson synthesis involves \(S_N2\) attack. It works best with primary alkyl halides.

Limitation: If secondary or tertiary alkyl halides are used, Elimination (forming alkenes) dominates over substitution because alkoxides are strong bases. Example: Reaction of Sodium methoxide with tert-butyl bromide gives isobutylene instead of ether.

By Acidic Dehydration with conc. \(H_2SO_4\) at 413 K.

Mechanism: 1. Protonation of alcohol. 2. \(S_N2\) attack by another alcohol molecule on protonated alcohol. 3. Loss of proton.

Secondary and tertiary alcohols form stable carbocations. At the high temperatures required for dehydration, elimination (to form alkenes) is favoured over substitution (to form ethers). Hence, alkenes are the major products.

The alkoxy group (\(-OR\)) is an activating group because the lone pair on oxygen enters into resonance with the benzene ring, increasing electron density. The resonance structures show increased negative charge density at ortho and para positions, making them ortho-para directing.

Reaction: \(CH_3-O-CH_3 + HI \to CH_3I + CH_3OH\).

1. Protonation: \(CH_3-O-CH_3 + H^+ \to CH_3-O^+(H)-CH_3\).
2. Nucleophilic Attack: \(I^-\) attacks the less sterically hindered methyl group via \(S_N2\). \(I^- + CH_3-O^+(H)-CH_3 \to CH_3I + CH_3OH\).

• (i) Styrene + \(H_2O/H^+\).
• (ii) Methylenecyclohexane + \(B_2H_6, H_2O_2/OH^-\).
• (iii) Pent-1-ene + \(H_2O/H^+\).
• (iv) Cyclohexene + \(H_2O/H^+\).

Step 1: Protonation of alcohol.

Step 2: Loss of water forms a \(2^\circ\) carbocation: \(CH_3-CH(CH_3)-CH^+-CH_3\).

Step 3 (Rearrangement): A 1,2-Hydride shift occurs from the adjacent tertiary carbon to form a more stable \(3^\circ\) carbocation: \(CH_3-C^+(CH_3)-CH_2-CH_3\).

Step 4: Attack of \(Br^-\) forms 2-Bromo-2-methylbutane.