JEE Chemistry Haloalkanes and Haloarenes MCQs Set 08

Answer: (a) \( \ce{C2H5Br} \) reacts with alcoholic KOH to form \( \ce{C2H5OH} \)

Explanation:
1. Alcoholic KOH gives ethene by elimination; aqueous KOH gives ethanol.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (b) Carbonyl chloride

Explanation:
1. Slow oxidation gives phosgene, \( \ce{COCl2} \).

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (b) \( \ce{C6H5CH2Cl} \)

Explanation:
1. Only benzylic (alkyl-type) halide is hydrolysed by aqueous NaOH under these conditions to give Cl-; aryl halides do not react.

Teacher's Note:
1. Aryl and vinyl halides are inert in ordinary nucleophilic substitution because the C-X bond has partial double-bond character.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (a) Dow's process

Explanation:
1. High-temperature, high-pressure hydrolysis of chlorobenzene with NaOH is Dow's process for phenol.

Teacher's Note:
1. Aryl and vinyl halides are inert in ordinary nucleophilic substitution because the C-X bond has partial double-bond character.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (b) Ethanol

Explanation:
1. Ethanol is an alcohol, not a halide.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (b) \( \ce{C6H5NH2} \)

Explanation:
1. Carbylamine test: only a primary amine (aniline) gives the foul-smelling isocyanide.

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (d) \( \ce{C2H5CN} \) and \( \ce{C2H5COOH} \)

Explanation:
1. \( \ce{C2H5Cl + KCN -> C2H5CN} \); hydrolysis of the nitrile gives propanoic acid.

Teacher's Note:
1. Ionic cyanide and nitrite attack through C and O/N respectively differently from the covalent silver salts: KCN gives nitriles, AgCN isocyanides, KNO2 nitrites and AgNO2 nitro compounds.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (a) \( \ce{C2H5OH} \)

Explanation:
1. Ethanol is oxidised to ethanal, which has the \( \ce{CH3CO-} \) group.

Teacher's Note:
1. The iodoform test is given by compounds with a CH3CO- or CH3CH(OH)- group; methanol, formaldehyde and diethyl ketone do not respond.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (b) Trichloromethane

Explanation:
1. Reimer-Tiemann reaction uses chloroform and aqueous NaOH (via dichlorocarbene).

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (b) \( \ce{CCl3NO2} \)

Explanation:
1. Chloropicrin (nitrochloroform), \( \ce{CCl3NO2} \), is formed.

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (c) \( \ce{AgNO3} \) solution

Explanation:
1. Pure chloroform gives no precipitate with \( \ce{AgNO3} \); a white precipitate would show that phosgene/HCl impurity is present.

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (c) An elimination reaction

Explanation:
1. A molecule of HX is removed.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (c) trans-Pent-2-ene

Explanation:
1. E2 elimination follows Saytzeff's rule, favouring the more substituted and more stable trans-pent-2-ene.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (b) o-Hydroxybenzoic acid

Explanation:
1. Ortho substitution gives salicylic acid (o-hydroxybenzoic acid).

Teacher's Note:
1. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (a) \( \ce{COCl2 + HCl} \)

Explanation:
1. \( \ce{2CHCl3 + O2 -> 2COCl2 + 2HCl} \).

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (a) Elimination

Explanation:
1. Alcoholic KOH (strongly basic, less nucleophilic medium) promotes E2 elimination.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (d) Chlorobenzene, vinyl chloride, chloroethane

Explanation:
1. Vinyl and aryl halides have the C-Cl bond strengthened by resonance and sp2 hybridisation and are very unreactive; chloroethane is much more reactive.

Teacher's Note:
1. Aryl and vinyl halides are inert in ordinary nucleophilic substitution because the C-X bond has partial double-bond character.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (b) Grignard's reagent

Explanation:
1. \( \ce{RX + Mg -> RMgX} \).

Teacher's Note:
1. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (d) All of these

Explanation:
1. Repeated alkylation gives a mixture of primary, secondary and tertiary amines and the quaternary salt.

Teacher's Note:
1. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (b) \( \ce{CH3-C#CH} \)

Explanation:
1. The strong base removes two molecules of HCl (double dehydrohalogenation of the gem-dihalide) to form propyne.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (a) Acetylene

Explanation:
1. \( \ce{2CHCl3 + 6Ag -> C2H2 + 6AgCl} \).

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (b) It gives nitroethane on heating with aqueous ethanolic \( \ce{AgNO2} \)

Explanation:
1. AgNO2 gives the nitroalkane.
2. Na gives butane (Wurtz), alcoholic KOH gives ethene, and silver acetate gives ethyl acetate.

Teacher's Note:
1. Wurtz coupling joins two alkyl groups with sodium in dry ether; fluorides do not react and mixed halides give a mixture of alkanes.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (d) Resonance stabilisation and sp2 hybridisation of C attached to halide

Explanation:
1. Lone-pair delocalisation into the ring and the shorter sp2-C-Cl bond give partial double bond character.

Teacher's Note:
1. SN1 follows carbocation stability (3 degree > 2 degree > 1 degree), while SN2 is fastest for the least crowded carbon.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (c) Methyl acetate

Explanation:
1. \( \ce{CH3Cl + CH3COOAg -> CH3COOCH3 + AgCl} \).

Teacher's Note:
1. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (d) 4

Explanation:
1. The molecule is symmetric: distinct carbons are the two terminal methyls (equivalent), C2/C6 (CH), C3/C5 (CH2) and C4 (CH2), so 4 monochloro derivatives.

Teacher's Note:
1. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (b) Resonance stabilisation

Explanation:
1. The chlorine lone pair conjugates with the double bond, giving the C-Cl bond partial double-bond character.

Teacher's Note:
1. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (b) Propionic acid

Explanation:
1. Hydrolysis of ethyl cyanide gives propanoic (propionic) acid.

Teacher's Note:
1. Ionic cyanide and nitrite attack through C and O/N respectively differently from the covalent silver salts: KCN gives nitriles, AgCN isocyanides, KNO2 nitrites and AgNO2 nitro compounds.
2. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (a) \( \ce{CHCl3} \) does not ionise in water

Explanation:
1. Chloroform is covalent and does not furnish Cl- ions.

Teacher's Note:
1. Chloroform is oxidised by air and light to poisonous phosgene, so it is stored in dark, full bottles with a little ethanol.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.