Alcohols, Phenols, and Ethers (Class 12 NCERT) Revision Notes

 over 100 short question-and-answer pairs covering the essential concepts, preparation, properties, and reactions from the NCERT Class 12 Chemistry Chapter:

Short Q&A for Alcohols, Phenols, and Ethers (Class 12 NCERT)

Part 1: Classification and Nomenclature

Q. No.	Question	Answer
1	Define an Alcohol.	A compound where the OH group is attached to an sp3-hybridized carbon atom in an aliphatic chain.
2	Define a Phenol.	A compound where the OH group is attached directly to an sp2-hybridized carbon atom of a benzene ring.
3	Define an Ether.	A compound containing an oxygen atom bridging two alkyl or aryl groups (R−O−R′).
4	Classify CH3​CH2​OH as 1∘,2∘, or 3∘ alcohol.	Primary (1∘) alcohol.
5	Classify an alcohol where the OH group is attached to a carbon bonded to three other carbon atoms.	Tertiary (3∘) alcohol.
6	What are Vinylic Alcohols?	Alcohols where the OH group is attached to a sp2 carbon of a double bond (generally unstable).
7	What is the common name for Benzene-1,2-diol?	Catechol.
8	What is the common name for Propane-1,2,3-triol?	Glycerol (or Glycerine).
9	What is the IUPAC name for the common anaesthetic, Et-O-Et?	Ethoxyethane.
10	What is the IUPAC name for m-cresol?	3-Methylphenol.
11	What are Allylic Alcohols?	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

Q. No.	Question	Answer
12	What is the industrial method for preparing ethanol from ethene?	Acid-catalyzed Hydration of alkenes (following Markownikoff's rule).
13	What is the product when an aldehyde is reduced with LiAlH4​?	Primary (1∘) alcohol.
14	What is the product when a ketone is reduced with NaBH4​?	Secondary (2∘) alcohol.
15	What is the product when a Grignard Reagent reacts with Formaldehyde (HCHO)?	Primary (1∘) alcohol.
16	What is the product when a Grignard Reagent reacts with any other Aldehyde (RCHO)?	Secondary (2∘) alcohol.
17	What is the product when a Grignard Reagent reacts with a Ketone (R2​CO)?	Tertiary (3∘) alcohol.
18	What is the main commercial method for preparing Phenol?	Cumene Process (oxidation of isopropyl benzene).
19	Name the two products formed when Cumene is oxidized and then acidified.	Phenol and Acetone.
20	How is Phenol prepared from Benzene Diazonium Chloride?	By warming the salt with water (H2​O).
21	How is Phenol prepared from Chlorobenzene (Dow's Process)?	By heating with NaOH at high temperature and pressure (623 K,300 bar).

Part 3: Physical Properties and Acidity

Q. No.	Question	Answer
22	Why do alcohols have much higher boiling points than corresponding alkanes or ethers?	Presence of Intermolecular Hydrogen Bonding.
23	How does the boiling point of alcohols change with branching?	Decreases (due to reduced surface area and weaker H-bonding network).
24	Why are lower molecular weight alcohols soluble in water?	They can form H-bonds with water molecules.
25	Are alcohols acidic or basic?	They can act as both (Amphoteric), but are generally very weak acids.
26	Rank the acidity of 1∘,2∘, and 3∘ alcohols.	1∘>2∘>3∘ (due to the +I effect of alkyl groups).
27	How does the stability of the alkoxide ion (R-O−) affect the acidity of alcohol?	Greater stability of R-O− means stronger acid.
28	Why are Phenols significantly more acidic than alcohols?	The phenoxide ion (Ar-O−) is stabilized by resonance (delocalization of charge).
29	How does an electron-withdrawing group (-NO2​) affect the acidity of phenol?	Increases acidity (stabilizes the phenoxide ion).
30	How does an electron-donating group (-CH3​) affect the acidity of phenol?	Decreases acidity (destabilizes the phenoxide ion).
31	Where is the effect of an electron-withdrawing group most pronounced on phenol acidity?	At the Ortho and Para positions.
32	Which is a stronger acid: Phenol or p-Nitrophenol?	p-Nitrophenol (-NO2​ is a strong EWG).
33	Which is a stronger acid: Phenol or Carbonic Acid (H2​CO3​)?	Carbonic Acid (H2​CO3​).
34	What is the test used to distinguish between Phenols and Alcohols?	Neutral Ferric Chloride Test (Phenols give a violet/green color).

Part 4: Chemical Reactions of Alcohols and Phenols

Q. No.	Question	Answer
35	Which bond cleavage is involved when an alcohol acts as a Nucleophile?	C−O bond cleavage (R−OH).
36	Which bond cleavage is involved when an alcohol acts as an Acid?	O−H bond cleavage (R−O−H).
37	What is the product when an alcohol reacts with an active metal (e.g., Na)?	Sodium Alkoxide (R−O−Na+) and H2​ gas.
38	What is the product when ethanol is oxidized by acidified K2​Cr2​O7​?	Ethanoic acid (CH3​COOH) (strong oxidation).
39	What is the product when 1∘ alcohol is oxidized using PCC (Pyridinium Chlorochromate)?	Aldehyde (RCHO) (selective oxidation).
40	What is the product when a 3∘ alcohol is oxidized?	Oxidation requires harsh conditions and leads to ketones and carboxylic acids with fewer carbons.
41	What is the mechanism for the dehydration of alcohols to alkenes?	E1 mechanism (via carbocation formation).
42	What is the product of the dehydration of Butan-1-ol?	But-1-ene (minor) and But-2-ene (major, Saytzeff's product).
43	What is the product when Phenol is treated with Br2​ water?	2,4,6-Tribromophenol (white precipitate).
44	What is the product when Phenol is treated with Br2​ in CS2​ or CHCl3​?	o- and p-Bromophenol (monosubstitution).
45	What is the reaction where Phenol is oxidized by chromic acid?	Formation of p-Benzoquinone.
46	What is the main product when Phenol reacts with Zn dust?	Benzene (Reduction).
47	Name the reaction of Phenol with Chloroform and NaOH followed by acidification.	Reimer-Tiemann Reaction.
48	What is the main product of the Reimer-Tiemann reaction?	Salicylaldehyde (o-Hydroxybenzaldehyde).
49	Name the reaction of Phenol with CO2​ and NaOH followed by acidification.	Kolbe's Reaction.
50	What is the main product of the Kolbe's reaction?	Salicylic Acid (o-Hydroxybenzoic acid).
51	What is the product when Salicylic Acid reacts with Acetic Anhydride?	Aspirin (Acetylsalicylic Acid).
52	What is the Lucas Reagent?	Concentrated HCl and Anhydrous ZnCl2​.
53	What is the observation when a 3∘ alcohol is treated with Lucas reagent?	Immediate turbidity (due to formation of R−Cl).
54	What is the observation when a 1∘ alcohol is treated with Lucas reagent?	No turbidity at room temperature.

Part 5: Ethers: Preparation and Reactions

Q. No.	Question	Answer
55	What is the main method for preparing symmetrical and unsymmetrical ethers?	Williamson's Synthesis.
56	Write the general reaction for Williamson's Synthesis.	R−O−Na++R′−X→R−O−R′+NaX (SN​2 mechanism).
57	In Williamson's synthesis, which reactant must be a primary alkyl halide to avoid elimination?	The Alkyl Halide (R′−X).
58	Why must the alkyl halide be primary in Williamson's synthesis (for maximum yield)?	To minimize the competing Elimination (E2) reaction.
59	How can symmetrical ethers be prepared from alcohols?	Dehydration of alcohols using conc.H2​SO4​ at low temperature (413 K).
60	Why do ethers have lower boiling points than isomeric alcohols?	Ethers lack H-bonding between their own molecules.
61	Are ethers soluble in water?	Slightly, due to the formation of H-bonds with water molecules.
62	What is the characteristic reaction of Ethers?	Cleavage of C−O bond by concentrated acids (HX).
63	What is the major product when Diethyl Ether reacts with cold HI?	Ethyl Iodide (CH3​CH2​I) and Ethanol (CH3​CH2​OH).
64	What is the final product when Diethyl Ether reacts with excess hot HI?	Ethyl Iodide (only one product, all C−O bonds are cleaved).
65	In the cleavage of unsymmetrical ethers with HI, where does the I− attack (if 1∘/2∘ groups)?	The I− attacks the smaller alkyl group (SN​2 mechanism).
66	In the cleavage of unsymmetrical ethers with HI (if 3∘ group is present)?	The I− attacks the 3∘ carbon (SN​1 mechanism) due to stable 3∘ carbocation.
67	What is the common name for Methoxybenzene (Ph-O-CH3​)?	Anisole.
68	What is the orientation of the -OR group in aromatic electrophilic substitution (e.g., Anisole)?	Ortho and Para directing (strongly activating, +M effect).

Part 6: Conceptual and Miscellaneous

Q. No.	Question	Answer
69	Which is a stronger nucleophile: H2​O or OH−?	OH− (negatively charged species are generally stronger nucleophiles).
70	What is the role of the -OH group in the ring of phenol toward electrophilic substitution?	It activates the ring (o/p directing) due to +M effect.
71	Why must ethanol be mixed with anhydrous CuSO4​ before analysis?	To remove trace amounts of water (alcohol is hygroscopic).
72	Why does the preparation of Butan-2-ol from But-1-ene follow Markownikoff's rule?	It proceeds through the more stable 2∘ carbocation.
73	What is the final product when Glycol (ethane-1,2-diol) is oxidized by HIO4​ (Periodic acid)?	Formaldehyde (HCHO).
74	What is the IUPAC name of Picric Acid?	2,4,6-Trinitrophenol.
75	What are denatured alcohols?	Ethanol mixed with poisonous substances (like methanol) to make it unfit for drinking.
76	Why is Ethanol preferred over Methanol for use in thermometers (at low temperatures)?	Methanol has a much lower freezing point (≈−97∘C).
77	What type of isomers are Ethanol and Dimethyl Ether?	Functional Isomers (C2​H6​O).
78	Why is the O−H bond length in phenol shorter than in alcohol?	C is sp2 hybridized in phenol, making it more electronegative and drawing the O atom closer.
79	What is the effect of having an ortho-substituent on the boiling point of phenol?	Can lead to Intramolecular H-bonding, resulting in lower boiling point (steam volatility).
80	Name the reaction used to prepare Methyl Salicylate (Oil of Wintergreen).	Esterification of Salicylic Acid with Methanol.
81	What is the use of Glycol in cold countries?	As an antifreeze in car radiators.
82	What is the key functional group required for the Iodoform Test?	CH3​−CH(OH)− or CH3​−CO− group.
83	Does Methanol give a positive Iodoform Test?	No, it lacks the required CH3​CH(OH)− group.
84	What is the product when 2-Propanol reacts with I2​ and NaOH?	Iodoform (CHI3​).
85	Why is the C−O bond in phenol difficult to break compared to alcohol?	Due to partial double bond character arising from resonance.
86	In the dehydration of alcohols, what happens when T is high (443 K)?	Elimination (Alkene formation).
87	In the dehydration of alcohols, what happens when T is low (413 K)?	Substitution (Ether formation).
88	What is the limiting factor in the SN​2 reaction involved in Williamson's synthesis?	Steric Hindrance around the carbon of the R−X bond.
89	Which type of cleavage (SN​1 or SN​2) occurs in the reaction of t-Butyl Methyl Ether with HI?	SN​1 (due to stable t-Butyl carbocation).
90	What are Crown Ethers?	Cyclic polyethers known for their ability to complex with metal ions.
91	What is the IUPAC name for Glycerol?	Propane-1,2,3-triol.
92	What is the common name for the reaction of Phenol with Phthalic Anhydride?	Phthalein Reaction (used as a test for Phenols).
93	What is the structural difference between p-cresol and Benzyl Alcohol (C6​H5​CH2​OH)?	p-cresol is a phenol; Benzyl Alcohol is an alcohol.
94	What is the product of the reduction of Phenol with H2​/Ni?	Cyclohexanol.
95	What is the role of H2​SO4​ in the Esterification reaction of alcohols?	Acts as a catalyst and a dehydrating agent (removes water).
96	Name the catalyst used for the dehydrogenation of 1∘ alcohol to aldehyde.	Heated Copper (Cu) at 573 K.
97	Name the catalyst used for the dehydrogenation of 2∘ alcohol to ketone.	Heated Copper (Cu) at 573 K.
98	What happens when a 3∘ alcohol is passed over Cu at 573 K?	Dehydration occurs (forming an alkene).
99	What is the most common use of Bisphenol A (BPA)?	To manufacture polycarbonate plastics and epoxy resins.
100	What is the final product when Ethanol is passed over heated Al2​O3​ at 623 K?	Ethene (C2​H4​) (Dehydration).
101	Which is more volatile: o-Nitrophenol or p-Nitrophenol?	o-Nitrophenol (Intramolecular H-bonding, lower BP).
102	Which exhibits intermolecular H-bonding: o-Nitrophenol or p-Nitrophenol?	p-Nitrophenol (can bond with neighboring molecules).
103	What is the common name of the product formed by the nitration of phenol?	Picric Acid (2,4,6-Trinitrophenol).
104	What is the difference in bonding between the OH group in alcohol and phenol?	Alcohol: C−O bond is sp3−O; Phenol: C−O bond is sp2−O.
105	What is the IUPAC name of ortho-hydroxybenzoic acid?	Salicylic Acid.
106	Why does Di-tert-butyl Ether react slowly with HI?	Steric hindrance prevents HI attack.