Q: The decreasing order of boiling points of alkyl halides is:

$ R I>R B r>R C l>R F $. Boiling points of alkyl halides increase as the halogen becomes larger and more polarizable, because London dispersion forces become stronger. Thus the order is RI > RBr > RCl > RF.

Q: For (i) I−, (ii) Cl−, (iii) Br−, the increasing order of nucleophilicity would be:

Cl− < Br− < I−. Nucleophilicity increases down the group in the periodic table due to the larger size and higher polarizability of the halide ions. Hence, I− is the most nucleophilic, followed by Br−, and then Cl−.

Q: The replacement of chlorine of chlorobenzene to give phenol requires drastic conditions, but the chlorine of 2,4-dinitrochlorobenzene is readily replaced since:

Nitro groups withdraw electrons from ortho/para positions of the aromatic ring. The nitro groups are strong electron-withdrawing groups and significantly reduce the electron density at the ortho and para positions of the aromatic ring, making the chlorine more susceptible to nucleophilic substitution.

Q: Chlorobenzene reacts with Mg in dry ether to give a compound (A) which further reacts with ethanol to yield:

Benzene. Chlorobenzene reacts with Mg in dry ether to form phenyl magnesium chloride (Grignard reagent). When this reacts with ethanol, it forms benzene as the product due to the acidic nature of ethanol, which protonates the phenyl group.

Q: Which one is most reactive towards SN1 reaction?

C6H5C(CH3)2(C6H5)Br. The SN1 reaction proceeds via a carbocation intermediate, and the stability of the carbocation determines the reactivity. Option C forms a highly stable benzylic tertiary carbocation due to resonance and hyperconjugation, making it the most reactive.

Q: Chloropicrin is obtained by the reaction of:

nitric acid on chloroform. Chloropicrin (CCl3NO2) is formed when chloroform reacts with nitric acid under specific conditions, making option D correct.

Q: Industrial preparation of chloroform employs acetone and:

Chlorine gas. Chloroform is industrially prepared by the reaction of acetone with chlorine gas, which undergoes halogenation and subsequent hydrolysis.

Q: Since 2-methylpropan-2-ol generates 3° carbocation, therefore, it reacts fastest with HBr.

Greater the stability of the intermediate carbocation, more reactive is the alcohol.. The reactivity of alcohols with HBr depends on the stability of the carbocation intermediate formed during the reaction. Tertiary alcohols like 2-methylpropan-2-ol form the most stable carbocation, making them react fastest.

Question 1

The decreasing order of boiling points of alkyl halides is:

Accepted Answer

$ R I>R B r>R C l>R F $. Boiling points of alkyl halides increase as the halogen becomes larger and more polarizable, because London dispersion forces become stronger. Thus the order is RI > RBr > RCl > RF.

Question 2

In an SN2 substitution reaction of the type R–Br + Cl− → R–Cl + Br−, which one of the following has the highest reactivity rate?

Accepted Answer

CH3CH2Br. CH3CH2Br has the least steric hindrance, allowing the nucleophile to attack the carbon more easily, leading to the highest reactivity rate.

Question 3

Which of the following reactions is an example of nucleophilic substitution reaction?

Accepted Answer

RX + KOH → ROH + KX. In the reaction RX + KOH → ROH + KX, the nucleophile OH⁻ replaces the halide ion X⁻ in the alkyl halide RX, making it a classic example of a nucleophilic substitution reaction.

Question 4

For (i) I−, (ii) Cl−, (iii) Br−, the increasing order of nucleophilicity would be:

Accepted Answer

Cl− < Br− < I−. Nucleophilicity increases down the group in the periodic table due to the larger size and higher polarizability of the halide ions. Hence, I− is the most nucleophilic, followed by Br−, and then Cl−.

Question 5

The replacement of chlorine of chlorobenzene to give phenol requires drastic conditions, but the chlorine of 2,4-dinitrochlorobenzene is readily replaced since:

Accepted Answer

Nitro groups withdraw electrons from ortho/para positions of the aromatic ring. The nitro groups are strong electron-withdrawing groups and significantly reduce the electron density at the ortho and para positions of the aromatic ring, making the chlorine more susceptible to nucleophilic substitution.

Question 6

Chlorobenzene reacts with Mg in dry ether to give a compound (A) which further reacts with ethanol to yield:

Accepted Answer

Benzene. Chlorobenzene reacts with Mg in dry ether to form phenyl magnesium chloride (Grignard reagent). When this reacts with ethanol, it forms benzene as the product due to the acidic nature of ethanol, which protonates the phenyl group.

Question 7

Which one is most reactive towards SN1 reaction?

Accepted Answer

C6H5C(CH3)2(C6H5)Br. The SN1 reaction proceeds via a carbocation intermediate, and the stability of the carbocation determines the reactivity. Option C forms a highly stable benzylic tertiary carbocation due to resonance and hyperconjugation, making it the most reactive.

Question 8

Chloropicrin is obtained by the reaction of:

Accepted Answer

nitric acid on chloroform. Chloropicrin (CCl3NO2) is formed when chloroform reacts with nitric acid under specific conditions, making option D correct.

Question 9

Industrial preparation of chloroform employs acetone and:

Accepted Answer

Chlorine gas. Chloroform is industrially prepared by the reaction of acetone with chlorine gas, which undergoes halogenation and subsequent hydrolysis.

Question 10

Since 2-methylpropan-2-ol generates 3° carbocation, therefore, it reacts fastest with HBr.

Accepted Answer

Greater the stability of the intermediate carbocation, more reactive is the alcohol.. The reactivity of alcohols with HBr depends on the stability of the carbocation intermediate formed during the reaction. Tertiary alcohols like 2-methylpropan-2-ol form the most stable carbocation, making them react fastest.

Question 11

The reaction CH₃—C—ONa + CH₂CH₂Cl → CH₃—C—O—CH₂—CH₃ is called:

Accepted Answer

Williamson Synthesis. The reaction involves the formation of an ether (CH₃—C—O—CH₂—CH₃) from an alkoxide (CH₃—C—ONa) and an alkyl halide (CH₂CH₂Cl), which is characteristic of the Williamson Synthesis.

Question 12

The reaction of ethyl magnesium bromide with water would give

Accepted Answer

Ethane. Ethyl magnesium bromide (a Grignard reagent) reacts with water to form ethane by replacing the magnesium bromide group with a hydrogen atom.

Question 13

Which one of the following reactions is expected to readily give a hydrocarbon product in good yields?

Accepted Answer

(CH₃)₃CCl —C₂H₅OH→. Option D represents a dehydrohalogenation reaction of a tertiary alkyl halide in the presence of ethanol, which readily forms an alkene (a hydrocarbon) in good yield due to the stability of the tertiary carbocation intermediate.

Question 14

Which of the following compounds will not undergo Friedel-Craft’s reaction easily?

Accepted Answer

Nitrobenzene. Nitrobenzene does not undergo Friedel-Craft's reaction easily because the nitro group is an electron-withdrawing group, which deactivates the benzene ring towards electrophilic substitution reactions.

Question 15

In the following reaction, C6H5CH2Br + Mg, Ether → X, the product ‘X’ is:

Accepted Answer

C6H5CH2CH2C6H5. The reaction involves the formation of a Grignard reagent (C6H5CH2MgBr) when benzyl bromide reacts with magnesium in the presence of ether. This reagent can further react to form a dimer, C6H5CH2CH2C6H5.

Question 16

Which of the following compounds reacts slower in electrophilic substitution?

Accepted Answer

C6H5NO2. Nitrobenzene (C6H5NO2) reacts slower in electrophilic substitution because the nitro group is an electron-withdrawing group, which deactivates the benzene ring by reducing its electron density.

Question 17

Elimination reaction of 2-Bromo-pentane to form pent-2-ene is:

Accepted Answer

Follows Zaitsev rule. The elimination reaction of 2-Bromo-pentane to form pent-2-ene is a β-elimination reaction, follows Zaitsev's rule (major product is the more substituted alkene), and is a dehydrohalogenation reaction. However, it is not a dehydration reaction as no water is removed.

Question 18

In an SN1 reaction on chiral centres there is:

Accepted Answer

Inversion more than retention leading to partial racemization. In an SN1 reaction, the intermediate is a planar carbocation, which allows attack from both sides. This leads to partial racemization, with inversion being slightly more favored due to steric factors.

Question 19

Which of the following compounds will undergo racemisation when solution of KOH hydrolyses?

Accepted Answer

(iv) CH3 
 | 
 CH 
 | 
 Cl 
 | 
 C2H5. Racemisation occurs when a compound has a chiral center and undergoes a reaction that leads to the formation of both enantiomers. Option (iv) has a chiral carbon (attached to CH3, Cl, H, and C2H5), making it capable of racemisation during hydrolysis.

Question 20

Consider the reactions:
(i) (CH3)2CH–CH2Br → C2H5OH
(CH3)2CH–CH2OCH2H5 + HBr
(ii) (CH3)2CH–CH2Br → C2H5O−
(CH3)2CH–CH2OCH2H5 + Br−
The mechanisms of reactions (i) and (ii) are respectively:

Accepted Answer

SN1 and SN2. Reaction (i) involves the formation of a carbocation intermediate, indicating an SN1 mechanism. Reaction (ii) proceeds via a direct nucleophilic substitution without intermediate formation, indicating an SN2 mechanism.

NEET Chemistry: Haloalkanes and Haloarenes questions with solutions

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