Alcohols, Phenols, and Ethers (Class 12 Chemistry) - Chemca

Alcohols, Phenols and Ethers

106 Short Q&A • NCERT Class 12 Chemistry

Class 12 JEE / NEET

106 Short Q&A Facts

Part 1: Classification and Nomenclature

Q1: Define an Alcohol.
A: A compound where the OH group is attached to an sp³-hybridized carbon atom in an aliphatic chain.
Q2: Define a Phenol.
A: A compound where the OH group is attached directly to an sp²-hybridized carbon atom of a benzene ring.
Q3: Define an Ether.
A: A compound containing an oxygen atom bridging two alkyl or aryl groups (R−O−R′).
Q4: Classify CH₃CH₂OH as 1°, 2°, or 3° alcohol.
A: Primary (1°) alcohol.
Q5: Classify an alcohol where the OH group is attached to a carbon bonded to three other carbon atoms.
A: Tertiary (3°) alcohol.
Q6: What are Vinylic Alcohols?
A: Alcohols where the OH group is attached to a sp² carbon of a double bond (generally unstable).
Q7: What is the common name for Benzene-1,2-diol?
A: Catechol.
Q8: What is the common name for Propane-1,2,3-triol?
A: Glycerol (or Glycerine).
Q9: What is the IUPAC name for the common anaesthetic, Et-O-Et?
A: Ethoxyethane.
Q10: What is the IUPAC name for m-cresol?
A: 3-Methylphenol.
Q11: What are Allylic Alcohols?
A: Alcohols where the OH group is attached to an sp³ C atom adjacent to a C=C double bond.

Part 2: Preparation of Alcohols and Phenols

Q12: What is the industrial method for preparing ethanol from ethene?
A: Acid-catalyzed Hydration of alkenes (following Markownikoff's rule).
Q13: What is the product when an aldehyde is reduced with LiAlH₄?
A: Primary (1°) alcohol.
Q14: What is the product when a ketone is reduced with NaBH₄?
A: Secondary (2°) alcohol.
Q15: What is the product when a Grignard Reagent reacts with Formaldehyde (HCHO)?
A: Primary (1°) alcohol.
Q16: What is the product when a Grignard Reagent reacts with any other Aldehyde (RCHO)?
A: Secondary (2°) alcohol.
Q17: What is the product when a Grignard Reagent reacts with a Ketone (R₂CO)?
A: Tertiary (3°) alcohol.
Q18: What is the main commercial method for preparing Phenol?
A: Cumene Process (oxidation of isopropyl benzene).
Q19: Name the two products formed when Cumene is oxidized and then acidified.
A: Phenol and Acetone.
Q20: How is Phenol prepared from Benzene Diazonium Chloride?
A: By warming the salt with water (H₂O).
Q21: How is Phenol prepared from Chlorobenzene (Dow's Process)?
A: By heating with NaOH at high temperature and pressure (623 K, 300 bar).

Part 3: Physical Properties and Acidity

Q22: Why do alcohols have much higher boiling points than corresponding alkanes or ethers?
A: Presence of Intermolecular Hydrogen Bonding.
Q23: How does the boiling point of alcohols change with branching?
A: Decreases (due to reduced surface area and weaker H-bonding network).
Q24: Why are lower molecular weight alcohols soluble in water?
A: They can form H-bonds with water molecules.
Q25: Are alcohols acidic or basic?
A: They can act as both (Amphoteric), but are generally very weak acids.
Q26: Rank the acidity of 1°, 2°, and 3° alcohols.
A: 1° > 2° > 3° (due to the +I effect of alkyl groups).
Q27: How does the stability of the alkoxide ion (R-O⁻) affect the acidity of alcohol?
A: Greater stability of R-O⁻ means stronger acid.
Q28: Why are Phenols significantly more acidic than alcohols?
A: The phenoxide ion (Ar-O⁻) is stabilized by resonance (delocalization of charge).
Q29: How does an electron-withdrawing group (-NO₂) affect the acidity of phenol?
A: Increases acidity (stabilizes the phenoxide ion).
Q30: How does an electron-donating group (-CH₃) affect the acidity of phenol?
A: Decreases acidity (destabilizes the phenoxide ion).
Q31: Where is the effect of an electron-withdrawing group most pronounced on phenol acidity?
A: At the Ortho and Para positions.
Q32: Which is a stronger acid: Phenol or p-Nitrophenol?
A: p-Nitrophenol (-NO₂ is a strong EWG).
Q33: Which is a stronger acid: Phenol or Carbonic Acid (H₂CO₃)?
A: Carbonic Acid (H₂CO₃).
Q34: What is the test used to distinguish between Phenols and Alcohols?
A: Neutral Ferric Chloride Test (Phenols give a violet/green color).

Part 4: Chemical Reactions of Alcohols and Phenols

Q35: Which bond cleavage is involved when an alcohol acts as a Nucleophile?
A: C−O bond cleavage (R−OH).
Q36: Which bond cleavage is involved when an alcohol acts as an Acid?
A: O−H bond cleavage (R−O−H).
Q37: What is the product when an alcohol reacts with an active metal (e.g., Na)?
A: Sodium Alkoxide (R−O−Na⁺) and H₂ gas.
Q38: What is the product when ethanol is oxidized by acidified K₂Cr₂O₇?
A: Ethanoic acid (CH₃COOH) (strong oxidation).
Q39: What is the product when 1° alcohol is oxidized using PCC (Pyridinium Chlorochromate)?
A: Aldehyde (RCHO) (selective oxidation).
Q40: What is the product when a 3° alcohol is oxidized?
A: Oxidation requires harsh conditions and leads to ketones and carboxylic acids with fewer carbons.
Q41: What is the mechanism for the dehydration of alcohols to alkenes?
A: E1 mechanism (via carbocation formation).
Q42: What is the product of the dehydration of Butan-1-ol?
A: But-1-ene (minor) and But-2-ene (major, Saytzeff's product).
Q43: What is the product when Phenol is treated with Br₂ water?
A: 2,4,6-Tribromophenol (white precipitate).
Q44: What is the product when Phenol is treated with Br₂ in CS₂ or CHCl₃?
A: o- and p-Bromophenol (monosubstitution).
Q45: What is the reaction where Phenol is oxidized by chromic acid?
A: Formation of p-Benzoquinone.
Q46: What is the main product when Phenol reacts with Zn dust?
A: Benzene (Reduction).
Q47: Name the reaction of Phenol with Chloroform and NaOH followed by acidification.
A: Reimer-Tiemann Reaction.
Q48: What is the main product of the Reimer-Tiemann reaction?
A: Salicylaldehyde (o-Hydroxybenzaldehyde).
Q49: Name the reaction of Phenol with CO₂ and NaOH followed by acidification.
A: Kolbe's Reaction.
Q50: What is the main product of the Kolbe's reaction?
A: Salicylic Acid (o-Hydroxybenzoic acid).
Q51: What is the product when Salicylic Acid reacts with Acetic Anhydride?
A: Aspirin (Acetylsalicylic Acid).
Q52: What is the Lucas Reagent?
A: Concentrated HCl and Anhydrous ZnCl₂.
Q53: What is the observation when a 3° alcohol is treated with Lucas reagent?
A: Immediate turbidity (due to formation of R−Cl).
Q54: What is the observation when a 1° alcohol is treated with Lucas reagent?
A: No turbidity at room temperature.

Part 5: Ethers: Preparation and Reactions

Q55: What is the main method for preparing symmetrical and unsymmetrical ethers?
A: Williamson's Synthesis.
Q56: Write the general reaction for Williamson's Synthesis.
A: R−O−Na⁺ + R′−X → R−O−R′ + NaX (SN² mechanism).
Q57: In Williamson's synthesis, which reactant must be a primary alkyl halide to avoid elimination?
A: The Alkyl Halide (R′−X).
Q58: Why must the alkyl halide be primary in Williamson's synthesis (for maximum yield)?
A: To minimize the competing Elimination (E2) reaction.
Q59: How can symmetrical ethers be prepared from alcohols?
A: Dehydration of alcohols using conc. H₂SO₄ at low temperature (413 K).
Q60: Why do ethers have lower boiling points than isomeric alcohols?
A: Ethers lack H-bonding between their own molecules.
Q61: Are ethers soluble in water?
A: Slightly, due to the formation of H-bonds with water molecules.
Q62: What is the characteristic reaction of Ethers?
A: Cleavage of C−O bond by concentrated acids (HX).
Q63: What is the major product when Diethyl Ether reacts with cold HI?
A: Ethyl Iodide (CH₃CH₂I) and Ethanol (CH₃CH₂OH).
Q64: What is the final product when Diethyl Ether reacts with excess hot HI?
A: Ethyl Iodide (only one product, all C−O bonds are cleaved).
Q65: In the cleavage of unsymmetrical ethers with HI, where does the I⁻ attack (if 1°/2° groups)?
A: The I⁻ attacks the smaller alkyl group (SN² mechanism).
Q66: In the cleavage of unsymmetrical ethers with HI (if 3° group is present)?
A: The I⁻ attacks the 3° carbon (SN¹ mechanism) due to stable 3° carbocation.
Q67: What is the common name for Methoxybenzene (Ph-O-CH₃)?
A: Anisole.
Q68: What is the orientation of the -OR group in aromatic electrophilic substitution (e.g., Anisole)?
A: Ortho and Para directing (strongly activating, +M effect).

Part 6: Conceptual and Miscellaneous

Q69: Which is a stronger nucleophile: H₂O or OH⁻?
A: OH⁻ (negatively charged species are generally stronger nucleophiles).
Q70: What is the role of the -OH group in the ring of phenol toward electrophilic substitution?
A: It activates the ring (o/p directing) due to +M effect.
Q71: Why must ethanol be mixed with anhydrous CuSO₄ before analysis?
A: To remove trace amounts of water (alcohol is hygroscopic).
Q72: Why does the preparation of Butan-2-ol from But-1-ene follow Markownikoff's rule?
A: It proceeds through the more stable 2° carbocation.
Q73: What is the final product when Glycol (ethane-1,2-diol) is oxidized by HIO₄ (Periodic acid)?
A: Formaldehyde (HCHO).
Q74: What is the IUPAC name of Picric Acid?
A: 2,4,6-Trinitrophenol.
Q75: What are denatured alcohols?
A: Ethanol mixed with poisonous substances (like methanol) to make it unfit for drinking.
Q76: Why is Ethanol preferred over Methanol for use in thermometers (at low temperatures)?
A: Methanol has a much lower freezing point (≈−97°C).
Q77: What type of isomers are Ethanol and Dimethyl Ether?
A: Functional Isomers (C₂H₆O).
Q78: Why is the O−H bond length in phenol shorter than in alcohol?
A: C is sp² hybridized in phenol, making it more electronegative and drawing the O atom closer.
Q79: What is the effect of having an ortho-substituent on the boiling point of phenol?
A: Can lead to Intramolecular H-bonding, resulting in lower boiling point (steam volatility).
Q80: Name the reaction used to prepare Methyl Salicylate (Oil of Wintergreen).
A: Esterification of Salicylic Acid with Methanol.
Q81: What is the use of Glycol in cold countries?
A: As an antifreeze in car radiators.
Q82: What is the key functional group required for the Iodoform Test?
A: CH₃−CH(OH)− or CH₃−CO− group.
Q83: Does Methanol give a positive Iodoform Test?
A: No, it lacks the required CH₃CH(OH)− group.
Q84: What is the product when 2-Propanol reacts with I₂ and NaOH?
A: Iodoform (CHI₃).
Q85: Why is the C−O bond in phenol difficult to break compared to alcohol?
A: Due to partial double bond character arising from resonance.
Q86: In the dehydration of alcohols, what happens when T is high (443 K)?
A: Elimination (Alkene formation).
Q87: In the dehydration of alcohols, what happens when T is low (413 K)?
A: Substitution (Ether formation).
Q88: What is the limiting factor in the SN² reaction involved in Williamson's synthesis?
A: Steric Hindrance around the carbon of the R−X bond.
Q89: Which type of cleavage (SN¹ or SN²) occurs in the reaction of t-Butyl Methyl Ether with HI?
A: SN¹ (due to stable t-Butyl carbocation).
Q90: What are Crown Ethers?
A: Cyclic polyethers known for their ability to complex with metal ions.
Q91: What is the IUPAC name for Glycerol?
A: Propane-1,2,3-triol.
Q92: What is the common name for the reaction of Phenol with Phthalic Anhydride?
A: Phthalein Reaction (used as a test for Phenols).
Q93: What is the structural difference between p-cresol and Benzyl Alcohol (C₆H₅CH₂OH)?
A: p-cresol is a phenol; Benzyl Alcohol is an alcohol.
Q94: What is the product of the reduction of Phenol with H₂/Ni?
A: Cyclohexanol.
Q95: What is the role of H₂SO₄ in the Esterification reaction of alcohols?
A: Acts as a catalyst and a dehydrating agent (removes water).
Q96: Name the catalyst used for the dehydrogenation of 1° alcohol to aldehyde.
A: Heated Copper (Cu) at 573 K.
Q97: Name the catalyst used for the dehydrogenation of 2° alcohol to ketone.
A: Heated Copper (Cu) at 573 K.
Q98: What happens when a 3° alcohol is passed over Cu at 573 K?
A: Dehydration occurs (forming an alkene).
Q99: What is the most common use of Bisphenol A (BPA)?
A: To manufacture polycarbonate plastics and epoxy resins.
Q100: What is the final product when Ethanol is passed over heated Al₂O₃ at 623 K?
A: Ethene (C₂H₄) (Dehydration).
Q101: Which is more volatile: o-Nitrophenol or p-Nitrophenol?
A: o-Nitrophenol (Intramolecular H-bonding, lower BP).
Q102: Which exhibits intermolecular H-bonding: o-Nitrophenol or p-Nitrophenol?
A: p-Nitrophenol (can bond with neighboring molecules).
Q103: What is the common name of the product formed by the nitration of phenol?
A: Picric Acid (2,4,6-Trinitrophenol).
Q104: What is the difference in bonding between the OH group in alcohol and phenol?
A: Alcohol: C−O bond is sp³−O; Phenol: C−O bond is sp²−O.
Q105: What is the IUPAC name of ortho-hydroxybenzoic acid?
A: Salicylic Acid.
Q106: Why does Di-tert-butyl Ether react slowly with HI?
A: Steric hindrance prevents HI attack.

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