Alcohols, Phenols and Ethers — Questions & Answers

Sample questions from Alcohols, Phenols and Ethers

1. Q1. A student wishes to make 2-methylbutan-2-ol from ethylmagnesium bromide. Which carbonyl compound must be used?

   • A.Propanal
   • B.Propanone✓
   • C.Butanone
   • D.Methanal
   Solution

   The target tertiary alcohol has the carbinol carbon bearing two methyl groups plus an ethyl group; removing the ethyl group contributed by the Grignard reagent leaves a carbonyl carbon carrying two methyl groups, that is, propanone (acetone).

2. Q2. Anisole is treated with CH3COCl and anhydrous AlCl3. Which statement about the product is correct?

   • A.3-Methoxyacetophenone is formed because OCH3 is a meta director
   • B.Phenol is obtained by cleavage of the ether
   • C.No reaction occurs because anisole is deactivated
   • D.4-Methoxyacetophenone is the major product because the methoxy group is an ortho/para director and the para position is least hindered✓
   Solution

   The methoxy group donates its oxygen lone pair into the ring, raising electron density at the ortho and para positions and making anisole more reactive than benzene; the bulky acylium electrophile and the bulky OCH3 group together make attack at the para position strongly preferred, so 4-methoxyacetophenone dominates.

3. Q3. Industrial phenol manufacture by the cumene process begins with which raw materials?

   • A.Benzene and propene✓
   • B.Toluene and methanol
   • C.Chlorobenzene and sodium hydroxide
   • D.Benzenesulphonic acid and steam
   Solution

   The cumene process starts with Friedel-Crafts alkylation of benzene with propene to give cumene (isopropylbenzene), which is then air-oxidised to cumene hydroperoxide before acid cleavage yields phenol and acetone.

4. Q4. Which of these alcohols will give the fastest dehydration on warming with 20 per cent H3PO4?

   • A.Ethanol
   • B.Propan-1-ol
   • C.2-Methylbutan-2-ol✓
   • D.2,2-Dimethylpropan-1-ol
   Solution

   Dehydration rate follows the stability of the carbocation formed in the slow step; only 2-methylbutan-2-ol is tertiary, so it ionises most readily and dehydrates fastest, while the primary alcohols listed require far harsher conditions.

5. Q5. Which statement about the reaction of phenol with benzenediazonium chloride in mild alkali is correct?

   • A.No reaction occurs because phenol is not nucleophilic enough
   • B.Coupling occurs at the para position of phenol to give an orange azo dye✓
   • C.Phenol is oxidised to benzoquinone
   • D.Nitrogen is lost and biphenyl is formed
   Solution

   In mildly alkaline medium phenol exists largely as phenoxide, an activated ring that attacks the weakly electrophilic diazonium ion; substitution occurs mainly at the less hindered para position, giving p-hydroxyazobenzene, a coloured azo compound used as a dye.

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