80. Which reaction gives 2,2-dibromopropane?
[AIEEE Chemistry — 2007]
(A) Propene with one equivalent of HBr
(B) Propyne with two equivalents of HBr
(C) 1-Bromopropene with one equivalent of HBr
(D) Ethyne with two equivalents of HBr
Answer: (B) Propyne with two equivalents of HBr
Explanation: Adding two equivalents of hydrogen bromide to the terminal alkyne propyne follows the usual Markovnikov orientation. Both bromine atoms ultimately become attached to the middle carbon, yielding the geminal dibromide 2,2-dibromopropane. The other combinations do not yield that structural product.
79. Reaction of toluene with chlorine in the presence of ferric chloride mainly forms what?
[AIEEE Chemistry — 2007]
(A) Benzoyl chloride
(B) Benzyl chloride
(C) Ortho- and para-chlorotoluene
(D) Meta-chlorotoluene
Answer: (C) Ortho- and para-chlorotoluene
Explanation: Ferric chloride promotes electrophilic aromatic chlorination. The methyl group already attached to benzene activates the ring and directs substitution preferentially to its ortho and para positions. Side-chain chlorination to benzyl chloride is more characteristic of radical conditions such as ultraviolet irradiation.
78. Which C₅H₁₀ compound produces acetone on ozonolysis?
[AIPMT Chemistry — 2007]
(A) 3-Methyl-1-butene
(B) Cyclopentane
(C) 2-Methyl-1-butene
(D) 2-Methyl-2-butene
Answer: (D) 2-Methyl-2-butene
Explanation: Ozonolysis cleaves an alkene double bond, converting each of its carbons into a carbonyl carbon. In 2-methyl-2-butene, one alkene carbon bears two methyl groups and therefore becomes acetone. The other cleavage fragment is ethanal.
77. Which listed polymer is manufactured by condensation polymerisation?
[AIPMT Chemistry — 2007]
(A) Teflon
(B) Natural rubber
(C) Styrene
(D) Nylon-6,6
Answer: (D) Nylon-6,6
Explanation: Nylon-6,6 is a polyamide produced by condensation between a diamine and a dicarboxylic acid, creating amide links while eliminating small molecules. Teflon and natural rubber form by addition polymerisation. Styrene is a monomer, rather than the requested condensation polymer.
76. An optically active compound shows zero net rotation despite having a chiral structure. What may explain this?
[AIPMT Chemistry — 2007]
(A) It must be a meso compound
(B) There is no compound in the solvent
(C) The sample may be a racemic mixture
(D) The molecule must be achiral
Answer: (C) The sample may be a racemic mixture
Explanation: An equimolar mixture of two enantiomers is racemic. Each enantiomer rotates plane-polarised light by an equal magnitude in the opposite direction, so the net observed rotation is zero. The underlying molecules remain chiral even though their combined solution is optically inactive.
75. What is the increasing nucleophilicity order of Cl⁻, Br⁻ and I⁻ in a polar protic solvent?
[AIPMT Chemistry — 2007]
(A) Cl⁻ < Br⁻ < I⁻
(B) I⁻ < Cl⁻ < Br⁻
(C) Br⁻ < Cl⁻ < I⁻
(D) I⁻ < Br⁻ < Cl⁻
Answer: (A) Cl⁻ < Br⁻ < I⁻
Explanation: In a polar protic medium smaller halide ions are more strongly solvated by hydrogen bonding, reducing their availability to attack an electrophile. The larger iodide ion is less tightly solvated and is more nucleophilic than bromide or chloride. Solvent identity is essential to this trend.
74. Order the decreasing electrophilic substitution reactivity of benzene I, toluene II, chlorobenzene III and phenol IV.
[AIPMT Chemistry — 2007]
(A) II > IV > I > III
(B) IV > III > II > I
(C) IV > II > I > III
(D) I > II > III > IV
Answer: (C) IV > II > I > III
Explanation: The hydroxyl group in phenol strongly donates electrons by resonance, activating the ring. A methyl group in toluene also activates the ring, but less strongly. Benzene is the baseline, while chlorine deactivates its ring inductively. Thus phenol reacts fastest and chlorobenzene slowest.
73. Reduction with LiAlH4 of which compound can give a secondary amine?
[AIPMT Chemistry — 2007]
(A) Methyl isocyanide
(B) Acetamide
(C) Methyl cyanide
(D) Nitroethane
Answer: (A) Methyl isocyanide
Explanation: Isocyanides have the general structure R–N≡C and can be reduced to N-methyl-substituted amines. Methyl isocyanide therefore produces dimethylamine, a secondary amine. Acetamide, acetonitrile and nitroethane instead normally provide primary amines when fully reduced.
72. Ethanol is converted to ethyl iodide, then to its Grignard reagent and reacted with formaldehyde followed by water. Which alcohol forms?
[AIEEE Chemistry — 2007]
(A) Butanal
(B) Butan-1-ol
(C) Propan-1-ol
(D) Propanal
Answer: (C) Propan-1-ol
Explanation: Converting ethanol to an ethyl halide and then its Grignard reagent makes an ethyl nucleophile. Addition to formaldehyde introduces one further carbon atom, producing a primary propyl alcohol after work-up. This carbon-chain extension is characteristic of formaldehyde reactions with Grignard reagents.
71. What is formed by oxidising ethylbenzene with hot potassium permanganate?
[AIEEE Chemistry — 2007]
(A) Benzophenone
(B) Acetophenone
(C) Benzoic acid
(D) Benzyl alcohol
Answer: (C) Benzoic acid
Explanation: Hot potassium permanganate oxidises an alkylbenzene side chain bearing a benzylic hydrogen to a carboxyl group. Ethylbenzene has such a hydrogen, so its two-carbon side chain is ultimately converted into the –COOH group of benzoic acid.
