Acidity: Alcohol vs Phenol vs Water
Phenol > Water > Alcohol
Phenol is more acidic because the phenoxide ion is stabilised by resonance with the benzene ring (negative charge delocalised over the ring). Electron-withdrawing groups (−NO₂, −Cl) on the ring increase acidity. Electron-donating groups (−CH₃, −OH) decrease it.
Must-Know Reactions
3° alcohol: immediate turbidity. 2° alcohol: turbidity within 5 min. 1° alcohol: no turbidity at room temperature. Used to distinguish alcohols.
1° alcohol → Aldehyde (PCC/mild) → Carboxylic Acid (KMnO₄/strong). 2° alcohol → Ketone. 3° alcohol → Resistant to oxidation (no α-H on the side with OH).
Alkoxide ion (R−O⁻) + primary alkyl halide (SN2) → ether. Use a 2° or 3° alkyl halide and you get elimination instead of substitution (E2 dominates). Critical distinction for NEET MCQs.
Kolbe's reaction: Phenol + CO₂/NaOH → Salicylic acid (sodium phenoxide + CO₂ at high T/P). Reimer-Tiemann: Phenol + CHCl₃/NaOH → Salicylaldehyde (CHO group added ortho to OH).
The H-Bonding Trap
Students often forget that ethers cannot form H-bonds with themselves (no O−H bond) but CAN accept H-bonds from other molecules (O has lone pairs). This explains why ethers have much lower boiling points than alcohols of similar molecular weight — a recurring NEET data-comparison question.
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