Haloalkanes & Haloarenes Test

Result

Haloalkanes & Haloarenes Test - 10

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Weekly Quiz Competition

Question 1
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Which of the following alkyl halides is respectively most and least electrophilic in S_N 1 reaction?

A
Both I and III

B
Both II and III

C
Both III and I

D
Both I and II

Solution

(III) forms tertiary carbocation, hence most reactive. (I) is least reactive as highly unstable carbocation is formed at bridge head carbon of bicyclic compound.
Question 2
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Which of the following is true regarding a S_N 1 reaction?

A
It would be faster at 25 °C than at 50 °C

B
it would be faster in ethanol than in pentane

C
Keeping the moles of reactants constant but doubling the quantity of solvent would decrease the rate by a factor of 4

D
Stereochemical inversion occurs exclusively

Solution

Protic solvents solvate carbocation, promotes S_N 1 reaction.
Question 3
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Rank the following molecules increasing in order of relative rate of SN1 solvolysis with methanol and heat.

A
Ill < II < IV < V < I

B
II < III < IV < I < V

C
V < IV < III < II < I

D
II < III < IV < V < I

Solution

(V) form s m ost stable, tertiary allylic, carbocation. (II) is vinylic halide, least reactive.
Question 4
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Which is the most likely product when the following iodide is heated with water?

A

B

C

D

Solution
Question 5
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What is the correct order of reactivity of the followings in hydrolysis reaction at elevated temperature?

A
I < II < III < IV

B
IV < III < II< I

C
I < III < IV < II

D
I < IV < III < II

Solution

(II) is most reactive as it forms aromatic carbocation (III) is next most reactive as it forms allylic carbocation. (I) is least reactive as it forms least stable cyclopropyl carbocation.
Question 6
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Statement Type

Direction : This section is based on Statement I and Statement II. Select the correct answer from the codes given below.

Q.

Consider the following two bromides I and II, undergoing solvolysis reaction in boiling ethanol :

Statement I : I is less reactive than II in the given solvolysis reaction.

Statement II : Resonance stabilisation available with the intermediate formed from II is the important driving force.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect

Solution

(II) forms more stable carbocation than (I).
Question 7
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Statement I : When 3-bromo propene, which contain a labelled ¹³ C at C-1 position is refluxed with methanol, following products were obtained.

Statement II : Methanol has an acidic proton bonded to oxygen.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect

Solution

Both statements are true but the two different products are due to resonance in carbocation intermediate as
Question 8
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One or More than One Options Correct Type

Direction : This section contains multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONE or MORE THAN ONE are correct.

Q.

What is/are true regarding a S_N 1 reaction?

A
Rate of reaction is faster in H₂ O than in C₂ H₅ OH

B
The reaction usually have more than one transition states

C
If α-carbon is chiral, partial racemisation and net inversion takes place

D
All are correct

Solution

H₂ O has higher solvating power than CH₃ CH₂ OH,hence faster S_N 1 reaction occur in H₂ O. Reaction proceeds via carbocation intermediate, it passes through more than one transition states. Due to the presence of some intimate ion pair, S_N 1 reaction occur resulting in partial racemisation and net inversion of configuration.
Since, nucleophile is not involved in rate determining step, reaction occur at same rate with both CH₃ —¹⁸ OH and CH₃ OH.
Question 9
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When the reactants shown below undergo substitution, which of the products will form?

A

B

C

D
All are correct

Solution

(I) gives (a) and (b) while (II) gives (c) and (d).
Question 10
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If a pure dextrorotatory enantiomer of the substrate of the following reaction is boiled with water, the correct statement(s) regarding S_N 1 product(s) is/are

A
product would be pure laevorotatory

B
product would consists of both laevo and dextrorotatory enantiomers

C
product would be optically active with enantiomer of inverted configuration predominating

D
Option B,C are Correct

Solution

S_N 1 reaction takes place giving partial racemisation but net inversion of configuration at chiral α-carbon.