JEE Chemistry Haloalkanes and Haloarenes MCQs Set 07

Answer: (d) -COOH group

Explanation:
1. A Grignard reagent \( \ce{RMgX} \) would be destroyed by acidic groups like -COOH, so it cannot contain one.

Teacher's Note:
1. Grignard reagents need dry ether and are destroyed by water, alcohols and any acidic hydrogen.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (c) Isopropyl chloride

Explanation:
1. The C-Cl bond is stronger than C-Br or C-I, so the chlorides are less reactive; and the secondary chloride is hindered towards SN2 and less able to ionise than the bromide, so isopropyl chloride is the least reactive here.

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: (a) Less reactive than benzyl chloride

Explanation:
1. The C-Cl bond in chlorobenzene has partial double-bond character (resonance, sp2 carbon), so it is much less reactive than alkyl or benzyl halides.

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. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (a) Methyl chloride > propyl chloride > chlorobenzene

Explanation:
1. For SN2, methyl > primary alkyl (less steric hindrance); chlorobenzene is least reactive.

Teacher's Note:
1. SN1 follows carbocation stability (3 degree > 2 degree > 1 degree), while SN2 is fastest for the least crowded carbon.
2. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (b) A primary amine

Explanation:
1. The carbylamine reaction (isocyanide test) is specific to primary amines.

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) Carbon tetrachloride and sodium hydroxide

Explanation:
1. With \( \ce{CCl4} \) in place of \( \ce{CHCl3} \) the intermediate \( \ce{-CCl3} \) group is hydrolysed to -COOH, giving salicylic acid.

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. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (b) Magnesium and alkyl halide

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

Teacher's Note:
1. Grignard reagents need dry ether and are destroyed by water, alcohols and any acidic hydrogen.
2. Remember the ambident nucleophiles: KCN gives nitriles, AgCN gives isocyanides, KNO2 gives nitrites, AgNO2 gives nitroalkanes.

Answer: (d) Chloropicrin

Explanation:
1. Chloropicrin, \( \ce{CCl3NO2} \), is a tear/war gas; it is made from the chlorination/nitration of chloroform or picric acid.

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: (d) Nothing will happen

Explanation:
1. \( \ce{CCl4} \) is covalent and does not give Cl- ions, so no precipitate forms.

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: (c) Salicylic acid

Explanation:
1. The trichloromethyl group introduced ortho to OH is hydrolysed to COOH.

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. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (a) Phenyl isocyanide

Explanation:
1. Carbylamine reaction: \( \ce{C6H5NH2 + CHCl3 + 3KOH -> C6H5NC + 3KCl + 3H2O} \).

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) Acetaldehyde

Explanation:
1. \( \ce{CH3CHCl2} \) hydrolyses to the unstable gem-diol, which loses water to give \( \ce{CH3CHO} \).

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: (c) Wurtz's reaction

Explanation:
1. Coupling of two alkyl halides with sodium in dry ether is the Wurtz reaction.

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: (b) Saytzeff product

Explanation:
1. The more substituted alkene (2-butene) is the Saytzeff product.

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) Glycol

Explanation:
1. Both F atoms (on different carbons, \( \ce{FCH2CH2F} \)) are replaced by OH: ethylene glycol.

Teacher's Note:
1. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (b) Benzaldehyde

Explanation:
1. Mild oxidation of the CH2Cl group gives \( \ce{C6H5CHO} \).

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: (c) Chloride ion is not formed

Explanation:
1. \( \ce{CCl4} \) is covalent and does not furnish Cl- ions in solution.

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) \( \ce{HCOONa} \)

Explanation:
1. \( \ce{CHCl3 + 4NaOH -> HCOONa + 3NaCl + 2H2O} \).

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: (a) Tetraethyl lead

Explanation:
1. \( \ce{4C2H5Br + 4Na/Pb -> (C2H5)4Pb + 4NaBr + 3Pb} \), the antiknock compound.

Teacher's Note:
1. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (a) Nitroethane

Explanation:
1. Covalent AgNO2 attacks through N, giving nitroethane as the main product (KNO2 would give the nitrite ester).

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) \( \ce{CHCl3 + CH3COCH3} \)

Explanation:
1. Chloroform adds to acetone in the presence of base to give chloretone, \( \ce{(CH3)2C(OH)CCl3} \).

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. Chloroform, DDT, BHC and chloropicrin are asked repeatedly: memorise their preparations and uses.

Answer: (a) \( \ce{CH3-CH=CH2} \)

Explanation:
1. Alcoholic KOH brings about dehydrobromination giving propene.

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) X = KCN, Y = \( \ce{LiAlH4} \)

Explanation:
1. \( \ce{C2H5Br + KCN -> C2H5CN} \), then reduction with \( \ce{LiAlH4} \) gives \( \ce{C3H7NH2} \) (propylamine).

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. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (a) 1-Butene

Explanation:
1. Alcoholic KOH causes E2 elimination; from a primary halide the product is the terminal alkene.

Teacher's Note:
1. Alcoholic KOH eliminates HX to give the more substituted alkene (Saytzeff rule); aqueous KOH substitutes.
2. Chlorobenzene and vinyl chloride are unreactive because the C-Cl bond has partial double-bond character.

Answer: (c) \( \ce{CH2Br-C#C-CH2Br} \) with Zn, heat

Explanation:
1. Zn removes the two Br atoms from 1,4-dibromobut-2-yne, creating cumulene \( \ce{CH2=C=C=CH2} \).

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: (c) Phenol

Explanation:
1. Dow-type substitution gives sodium phenoxide, which on acidification gives 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. Haloform and carbylamine reactions are tests; know the reagent, the product and the observation.

Answer: (c) Trichloroacetaldehyde

Explanation:
1. Chloral (trichloroacetaldehyde) condenses with two molecules of chlorobenzene.

Teacher's Note:
1. DDT is made from chloral and chlorobenzene with conc. sulphuric acid; it is a persistent insecticide.
2. Separate substitution (aqueous KOH, AgCN, KCN) from elimination (alcoholic KOH) before reading the options.

Answer: (c) Both (a) and (b)

Explanation:
1. Reimer-Tiemann formylation goes ortho (major) and para (minor), giving both aldehydes.

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.