Question 1

Which of the following compounds is classified as a primary alcohol?

Accepted Answer

Primary alcohols have the OH group attached to a carbon bonded to only one other carbon; CH₃CH₂OH (ethanol) fits this definition.

Question 2

What is the IUPAC name of the compound with structure CH₃OCH₂CH₃?

Accepted Answer

The IUPAC name for CH₃OCH₂CH₃ is methoxyethane, where methoxy is the substituent on the ethane backbone.

Question 3

Phenol is more acidic than aliphatic alcohols because:

Accepted Answer

Phenol's acidity arises from resonance stabilization of the phenoxide anion by the aromatic ring, making H⁺ loss easier.

Question 4

Which reagent is commonly used to distinguish between primary and secondary alcohols?

Accepted Answer

Acidic KMnO₄ oxidizes primary alcohols to carboxylic acids (decolorizes) and secondary to ketones, while tertiary alcohols are unaffected.

Question 5

The dehydration of ethanol (C₂H₅OH) with concentrated H₂SO₄ at 170°C produces:

Accepted Answer

Dehydration of ethanol at 170°C with concentrated H₂SO₄ removes water and forms ethene (C₂H₄) via an E1 mechanism.

Question 6

Which of the following alcohols undergoes dehydration most readily?

Accepted Answer

Tertiary alcohols form the most stable carbocation intermediate, making them most reactive towards dehydration.

Question 7

What is the main structural difference between phenol and ethanol?

Accepted Answer

Phenol has the hydroxyl group (-OH) directly attached to an aromatic benzene ring, whereas ethanol has -OH attached to an aliphatic carbon.

Question 8

Which of the following correctly represents the order of acidic strength?

Accepted Answer

Phenol is acidic due to resonance stabilization of the phenoxide ion, while alcohols are weakly acidic with strength decreasing from primary to tertiary.

Question 9

When ethanol is treated with acidified potassium permanganate, the primary product is:

Accepted Answer

Acidified potassium permanganate oxidizes ethanol first to acetaldehyde and further to acetic acid.

Question 10

Phenol reacts with sodium hydroxide to form sodium phenoxide because:

Accepted Answer

The aromatic ring's resonance effect stabilizes the negative charge on the phenoxide ion, making phenol weakly acidic and capable of reacting with bases.

Question 11

The ether linkage (-O-) in ethers is formed by elimination of water between two alcohol molecules. This reaction is known as:

Accepted Answer

Intermolecular dehydration occurs when two alcohol molecules lose water under acidic conditions with heat to form an ether.

Question 12

Which property distinguishes ethers from alcohols?

Accepted Answer

Ethers lack a free -OH group, so they cannot act as hydrogen bond donors, resulting in lower water solubility compared to alcohols.

Question 13

Tertiary butanol (2-methylpropan-2-ol) does not undergo oxidation with mild oxidizing agents because:

Accepted Answer

Tertiary alcohols lack hydrogen atoms on the carbon bearing the hydroxyl group, which is essential for oxidation, so they resist oxidation by mild reagents.

Question 14

Phenol is significantly more acidic than aliphatic alcohols. Which of the following BEST explains this phenomenon?

Accepted Answer

Resonance stabilization of the phenoxide anion (negative charge delocalized across aromatic ring) makes phenol's conjugate base much more stable, lowering its pKa to ~10 compared to ~15-16 for aliphatic alcohols.

Question 15

When ethanol is treated with excess concentrated H₂SO₄ at 140°C, the major product formed is diethyl ether. Which mechanism describes this reaction?

Accepted Answer

Protonated ethanol (C₂H₅-OH₂⁺) acts as a leaving group; a second ethanol molecule attacks the carbocation intermediate (SN1-type mechanism) to form diethyl ether and water.

Question 16

The pKa values of three compounds are: phenol (10.0), m-nitrophenol (8.4), and p-nitrophenol (7.1). What is the correct order of their acid strength?

Accepted Answer

Lower pKa indicates stronger acid; the nitro group (-NO₂), an electron-withdrawing group, stabilizes the phenoxide anion better when in para position than meta, making p-nitrophenol most acidic.

NDA Alcohols Phenols & Ethers

Alcohols Phenols & Ethers — Practice Questions