Multiple Choice Questions (MCQs)

Multiple Choice Questions (MCQs) and Explanations

Here are 40 MCQs based on the “Alcohols, Phenols, and Ethers” notes, with detailed explanations.

Question 1: Which of the following is a primary alcohol? (A) 2-methylpropan-2-ol (B) Butan-2-ol (C) 2-methylpropan-1-ol (D) Propan-2-ol

Explanation 1:

  • Correct Answer: (C)
  • Reasoning: A primary alcohol has the -OH group attached to a primary carbon atom. 2-methylpropan-1-ol ((CH3​)2​CHCH2​OH) has the -OH group on a CH2​ group, which is a primary carbon. (A) is tertiary, (B) and (D) are secondary.

Question 2: The boiling point of ethanol is higher than that of methoxymethane (dimethyl ether) due to: (A) Higher molecular mass of ethanol. (B) Formation of intermolecular hydrogen bonds in ethanol. (C) Ethanol being a polar molecule. (D) Resonance in ethanol.

Explanation 2:

  • Correct Answer: (B)
  • Reasoning: Alcohols can form strong intermolecular hydrogen bonds due to the presence of the highly polar -OH group. Ethers, while polar, cannot form intermolecular hydrogen bonds among themselves (they can act as H-bond acceptors but not donors). This strong H-bonding in ethanol requires more energy to overcome, leading to a higher boiling point. Their molecular masses are comparable (C2​H6​O for both).

Question 3: Which of the following reagents is used for the selective oxidation of a primary alcohol to an aldehyde? (A) Acidified KMnO4​ (B) Alkaline KMnO4​ (C) Pyridinium Chlorochromate (PCC) (D) K2​Cr2​O7​/H+

Explanation 3:

  • Correct Answer: (C)
  • Reasoning: PCC is a mild oxidizing agent that oxidizes primary alcohols to aldehydes without further oxidizing them to carboxylic acids. All other options (A, B, D) are strong oxidizing agents that would oxidize primary alcohols to carboxylic acids.

Question 4: Phenols are more acidic than alcohols because: (A) Phenoxide ion is more stable than alkoxide ion due to resonance. (B) Phenols have a benzene ring. (C) Oxygen in phenols is sp2 hybridized. (D) Phenols have a higher boiling point.

Explanation 4:

  • Correct Answer: (A)
  • Reasoning: The phenoxide ion, formed after the deprotonation of phenol, is resonance stabilized by the delocalization of the negative charge over the benzene ring. This stabilization makes it easier for phenol to lose a proton, thus increasing its acidity compared to alcohols, where the alkoxide ion is not resonance stabilized.

Question 5: Williamson synthesis is used to prepare: (A) Alcohols (B) Phenols (C) Ethers (D) Esters

Explanation 5:

  • Correct Answer: (C)
  • Reasoning: Williamson synthesis is a key method for preparing both symmetrical and unsymmetrical ethers by reacting an alkyl halide with a sodium alkoxide.

Question 6: When propan-1-ol reacts with conc. H2​SO4​ at 443 K, the major product is: (A) Dipropyl ether (B) Propene (C) Propanal (D) Propanone

Explanation 6:

  • Correct Answer: (B)
  • Reasoning: Dehydration of alcohols with concentrated H2​SO4​ at higher temperatures (e.g., 443 K or 170∘C) favors elimination, leading to the formation of alkenes. At 413 K, ether formation is favored.

Question 7: Which of the following is most acidic? (A) p-nitrophenol (B) p-methylphenol (C) Phenol (D) p-methoxyphenol

Explanation 7:

  • Correct Answer: (A)
  • Reasoning: Electron-withdrawing groups (like −NO2​) increase the acidity of phenols by stabilizing the phenoxide ion through resonance and inductive effects. Electron-donating groups (like −CH3​, −OCH3​) decrease acidity. Therefore, p-nitrophenol is the most acidic among the choices.

Question 8: The reaction of phenol with chloroform in the presence of aqueous NaOH followed by acid hydrolysis gives salicylaldehyde. This reaction is known as: (A) Kolbe’s reaction (B) Reimer-Tiemann reaction (C) Williamson synthesis (D) Wurtz reaction

Explanation 8:

  • Correct Answer: (B)
  • Reasoning: This is the Reimer-Tiemann reaction, which is used for the ortho-formylation of phenols, leading to salicylaldehyde. Kolbe’s reaction involves CO2​ to give salicylic acid.

Question 9: Grignard reagents react with formaldehyde to produce: (A) Primary alcohols (B) Secondary alcohols (C) Tertiary alcohols (D) Ketones

Explanation 9:

  • Correct Answer: (A)
  • Reasoning: The reaction of Grignard reagents with formaldehyde (HCHO) followed by hydrolysis yields primary alcohols. Other aldehydes give secondary alcohols, and ketones give tertiary alcohols.

Question 10: Aniline is converted to benzene diazonium chloride, which on warming with water gives: (A) Aniline (B) Benzoic acid (C) Phenol (D) Chlorobenzene

Explanation 10:

  • Correct Answer: (C)
  • Reasoning: Diazonium salts, when warmed with water, undergo hydrolysis to yield phenols. This is a common laboratory method for preparing phenols.

Question 11: What is the IUPAC name of isobutyl alcohol? (A) Butan-1-ol (B) Butan-2-ol (C) 2-methylpropan-1-ol (D) 2-methylpropan-2-ol

Explanation 11:

  • Correct Answer: (C)
  • Reasoning: Isobutyl alcohol has the structure (CH3​)2​CHCH2​OH. The longest carbon chain containing the -OH group is 3 carbons (propane), and a methyl group is at position 2. The -OH is at position 1. Hence, 2-methylpropan-1-ol.

Question 12: Which of the following is formed when phenol reacts with zinc dust on heating? (A) Benzene (B) Benzoic acid (C) Cyclohexanol (D) Anisole

Explanation 12:

  • Correct Answer: (A)
  • Reasoning: Phenol undergoes reduction with zinc dust on heating to form benzene and zinc oxide. This is a characteristic reaction of phenols.

Question 13: The common name for CH3​OCH2​CH3​ is: (A) Dimethyl ether (B) Diethyl ether (C) Ethyl methyl ether (D) Methoxyethane

Explanation 13:

  • Correct Answer: (C)
  • Reasoning: The two alkyl groups attached to the oxygen are ethyl and methyl. Following alphabetical order, it’s ethyl methyl ether. Methoxyethane is its IUPAC name.

Question 14: Which of the following is not a common industrial method for preparing ethanol? (A) Acid-catalyzed hydration of ethene (B) Fermentation of molasses (C) Hydroboration-oxidation of ethene (D) Fermentation of starch

Explanation 14:

  • Correct Answer: (C)
  • Reasoning: Hydroboration-oxidation is a laboratory method and not a large-scale industrial method for ethanol production. Acid-catalyzed hydration of ethene and fermentation are major industrial routes.

Question 15: Which of the following compounds would show a positive iodoform test? (A) Propan-1-ol (B) Propan-2-ol (C) Ethanol (D) Both (B) and (C)

Explanation 15:

  • Correct Answer: (D)
  • Reasoning: The iodoform test is positive for compounds containing the CH3​CH(OH) group (secondary alcohols) or the CH3​CO group (methyl ketones). Propan-2-ol has CH3​CH(OH) and Ethanol has CH3​CH(OH) (CH3​CH2​OH). Propan-1-ol does not have this group.

Question 16: The order of reactivity of alcohols towards reaction with HX is: (A) 1∘>2∘>3∘ (B) 3∘>2∘>1∘ (C) 2∘>1∘>3∘ (D) 1∘=2∘=3∘

Explanation 16:

  • Correct Answer: (B)
  • Reasoning: The reaction of alcohols with HX typically proceeds via an SN​1 mechanism for 2∘ and 3∘ alcohols (or SN​2 for 1∘). The rate-determining step for SN​1 is carbocation formation, and carbocation stability is 3∘>2∘>1∘. Hence, 3∘ alcohols are most reactive.

Question 17: Which of the following reagents can distinguish between phenol and ethanol? (A) Litmus paper (B) Neutral ferric chloride solution (C) Sodium metal (D) NaOH solution

Explanation 17:

  • Correct Answer: (B)
  • Reasoning: Phenols give a characteristic violet/purple/green color with neutral ferric chloride solution due to the formation of a colored complex. Alcohols do not give this test. Both react with sodium metal, and both are acidic enough to react with NaOH (though alcohols are very weak). Litmus would show both as acidic (though phenol is stronger).

Question 18: The main product obtained when diethyl ether is heated with excess concentrated HI is: (A) Ethanol (B) Iodoethane (C) Ethane (D) Ethylene

Explanation 18:

  • Correct Answer: (B)
  • Reasoning: Ethers undergo cleavage by hot concentrated HX. With excess HX, both alkyl groups are converted to alkyl halides. Diethyl ether will yield two molecules of iodoethane. CH3​CH2​OCH2​CH3​+2HIheat​2CH3​CH2​I+H2​O.

Question 19: What is the product when phenol is treated with concentrated HNO3​ and concentrated H2​SO4​? (A) Salicylic acid (B) 2,4,6-trinitrophenol (C) Nitrobenzene (D) o-nitrophenol

Explanation 19:

  • Correct Answer: (B)
  • Reasoning: Phenol, being highly activated by the -OH group, undergoes nitration with concentrated nitric acid in the presence of concentrated sulfuric acid to form 2,4,6-trinitrophenol, commonly known as Picric acid.

Question 20: Which solvent is used in Williamson synthesis? (A) Aqueous solution (B) Dry ether (C) Ethanol (D) Acetone

Explanation 20:

  • Correct Answer: (C)
  • Reasoning: Williamson synthesis usually involves a sodium alkoxide (which is often generated in alcohol) and an alkyl halide. The reaction is typically carried out in an alcoholic solvent.

Question 21: The boiling points of isomeric alcohols follow the order: (A) Primary > Secondary > Tertiary (B) Secondary > Primary > Tertiary (C) Tertiary > Secondary > Primary (D) Primary = Secondary = Tertiary

Explanation 21:

  • Correct Answer: (A)
  • Reasoning: As branching increases, the surface area available for van der Waals interactions decreases, leading to weaker intermolecular forces and thus lower boiling points. Primary alcohols are least branched, followed by secondary, then tertiary.

Question 22: The major product formed when phenol reacts with Br2​/H2​O is: (A) Bromobenzene (B) 2-bromophenol (C) 4-bromophenol (D) 2,4,6-tribromophenol

Explanation 22:

  • Correct Answer: (D)
  • Reasoning: In aqueous solution, phenol ionizes to phenoxide ion, which is extremely activated towards electrophilic substitution. As a result, all ortho and para positions are brominated, leading to the formation of 2,4,6-tribromophenol as a white precipitate.

Question 23: Methanol is industrially prepared from: (A) Fermentation of sugar (B) Reduction of formaldehyde (C) Synthesis gas (D) Oxidation of methane

Explanation 23:

  • Correct Answer: (C)
  • Reasoning: Methanol is industrially produced from “synthesis gas” (CO+H2​) by catalytic hydrogenation at high temperature and pressure.

Question 24: Which of the following is highly poisonous and can cause blindness or death? (A) Ethanol (B) Methanol (C) Diethyl ether (D) Ethylene glycol

Explanation 24:

  • Correct Answer: (B)
  • Reasoning: Methanol is highly poisonous. Even small amounts can be metabolized to formaldehyde and formic acid in the body, leading to severe acidosis, blindness, and death.

Question 25: How can ethoxybenzene be prepared by Williamson synthesis? (A) C6​H5​Br+CH3​CH2​ONa (B) CH3​CH2​Br+C6​H5​ONa (C) C6​H5​OH+CH3​CH2​Br (D) C6​H5​Br+CH3​CH2​OH

Explanation 25:

  • Correct Answer: (B)
  • Reasoning: For alkyl aryl ethers, the aryl group must be part of the alkoxide (phenoxide) and the alkyl group must come from a primary alkyl halide to ensure the reaction proceeds via SN​2 and avoids elimination. Therefore, CH3​CH2​Br (ethyl bromide) reacting with C6​H5​ONa (sodium phenoxide) will give ethoxybenzene.

Question 26: The product of oxidation of a secondary alcohol using PCC is: (A) Aldehyde (B) Ketone (C) Carboxylic acid (D) Alkene

Explanation 26:

  • Correct Answer: (B)
  • Reasoning: PCC oxidizes secondary alcohols to ketones. It’s a mild oxidant and doesn’t cause further oxidation or C-C bond cleavage.

Question 27: Which of the following reagents will convert cumene to phenol and acetone? (A) H2​O/H+ (B) KMnO4​/H+ (C) O2​/heat followed by H+/H2​O (D) NaOH/H+

Explanation 27:

  • Correct Answer: (C)
  • Reasoning: This describes the industrial preparation of phenol from cumene (isopropylbenzene). Cumene is oxidized by air (O2​) to cumene hydroperoxide, which then decomposes in the presence of acid (H+/H2​O) to yield phenol and acetone.

Question 28: Why are ethers not capable of forming intermolecular hydrogen bonds among themselves? (A) They are non-polar. (B) The oxygen atom is sp2 hybridized. (C) They do not have a hydrogen atom directly bonded to oxygen. (D) They have a very high boiling point.

Explanation 28:

  • Correct Answer: (C)
  • Reasoning: For intermolecular hydrogen bonding to occur, a hydrogen atom must be directly bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine. Ethers have C-O-C bonds, so there’s no H directly attached to O to donate an H-bond.

Question 29: The Kolbe’s reaction is used for the preparation of: (A) Salicylaldehyde (B) Salicylic acid (C) Benzene (D) Anisole

Explanation 29:

  • Correct Answer: (B)
  • Reasoning: Kolbe’s reaction (or Kolbe-Schmidt reaction) involves the reaction of sodium phenoxide with carbon dioxide under specific conditions, followed by acid hydrolysis, to yield salicylic acid (o-hydroxybenzoic acid).

Question 30: Which of the following conditions favors the formation of an alkene from an alcohol? (A) High concentration of nucleophile (B) Lower temperature with concentrated H2​SO4​ (C) High temperature with concentrated H2​SO4​ (D) Reaction with PCC

Explanation 30:

  • Correct Answer: (C)
  • Reasoning: Elimination reactions (like dehydration to form alkenes) are generally favored by higher temperatures. For alcohols and concentrated H2​SO4​, 443 K or 170∘C favors alkene formation, while 413 K or 140∘C favors ether formation.

Question 31: Which of the following is an example of a benzylic alcohol? (A) CH2​=CH−CH2​OH (B) C6​H5​OH (C) C6​H5​CH2​OH (D) CH3​CH2​OH

Explanation 31:

  • Correct Answer: (C)
  • Reasoning: A benzylic alcohol has the -OH group attached to an sp3 hybridized carbon atom that is directly attached to an aromatic ring. C6​H5​CH2​OH (benzyl alcohol) fits this description. (A) is allylic, (B) is phenol, (D) is a primary alcohol.

Question 32: The product formed when a tertiary alcohol is heated with copper at 573 K is: (A) Aldehyde (B) Ketone (C) Alkene (D) Ether

Explanation 32:

  • Correct Answer: (C)
  • Reasoning: Primary and secondary alcohols undergo dehydrogenation (oxidation) to aldehydes and ketones, respectively, when heated with copper at 573 K. However, tertiary alcohols undergo dehydration (elimination) under these conditions to form alkenes.

Question 33: Why is denatured alcohol prepared? (A) To increase its boiling point. (B) To make it unfit for drinking purposes. (C) To increase its density. (D) To make it a better solvent.

Explanation 33:

  • Correct Answer: (B)
  • Reasoning: Denatured alcohol is ethanol that has been made poisonous or unpalatable by adding substances like copper sulfate (for color) and pyridine (for foul smell), primarily to prevent its misuse as an alcoholic beverage and avoid taxation on beverage alcohol.

Question 34: The reaction RCOOHLiAlH4​​RCH2​OH is an example of: (A) Oxidation (B) Reduction (C) Substitution (D) Elimination

Explanation 34:

  • Correct Answer: (B)
  • Reasoning: Lithium aluminium hydride (LiAlH4​) is a strong reducing agent. It reduces carboxylic acids to primary alcohols.

Question 35: In electrophilic substitution reactions, the -OH group in phenol is: (A) Deactivating and ortho-para directing. (B) Activating and meta-directing. (C) Activating and ortho-para directing. (D) Deactivating and meta-directing.

Explanation 35:

  • Correct Answer: (C)
  • Reasoning: The -OH group in phenol is a strong activating group (due to resonance, it donates electron density to the ring) and is ortho-para directing for incoming electrophiles.

Question 36: Which of the following compounds is also known as “wood spirit”? (A) Ethanol (B) Methanol (C) Phenol (D) Diethyl ether

Explanation 36:

  • Correct Answer: (B)
  • Reasoning: Methanol (CH3​OH) was historically produced by the destructive distillation of wood, hence its common name “wood spirit.”

Question 37: What is the product of hydroboration-oxidation of propene? (A) Propan-1-ol (B) Propan-2-ol (C) Propanal (D) Propanoic acid

Explanation 37:

  • Correct Answer: (A)
  • Reasoning: Hydroboration-oxidation is an anti-Markovnikov addition of water to an alkene. For propene, it yields propan-1-ol (the -OH group adds to the less substituted carbon).

Question 38: The correct order of acidity for alcohols, water, and phenols is: (A) Alcohols < Water < Phenols (B) Water < Alcohols < Phenols (C) Phenols < Alcohols < Water (D) Alcohols < Phenols < Water

Explanation 38:

  • Correct Answer: (A)
  • Reasoning: Alcohols are the least acidic (alkoxide ion is destabilized by +I effect). Water is more acidic than alcohols. Phenols are more acidic than water due to resonance stabilization of the phenoxide ion, but less acidic than carboxylic acids.

Question 39: When an alkyl aryl ether (e.g., anisole) is cleaved by concentrated HI, the products are: (A) Alkyl iodide and aryl iodide. (B) Phenol and alkyl iodide. (C) Alkyl iodide and alcohol. (D) Phenol and alcohol.

Explanation 39:

  • Correct Answer: (B)
  • Reasoning: In the cleavage of alkyl aryl ethers with HI, the aryl-oxygen bond does not break due to its partial double bond character. The alkyl-oxygen bond breaks. So, phenol and an alkyl iodide are formed.

Question 40: What is the primary environmental concern associated with Freons? (A) Causing acid rain. (B) Contributing to global warming. (C) Depleting the ozone layer. (D) Causing eutrophication.

Explanation 40:

  • Correct Answer: (C)
  • Reasoning: Freons (CFCs) are well-known for their role in the depletion of the stratospheric ozone layer, which protects Earth from harmful UV radiation.

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