Haloalkanes and Haloarenes Test 9

Result

Haloalkanes and Haloarenes Test 9

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Weekly Quiz Competition

Question 1
1 / -0

Only One Option Correct Type
Direction (Q. Nos. 1-8) This section contains 8 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct.
Q.
Which of the S_N2 reaction is fastest?

A

B

C

D

Solution

CH₃ Br is more reactive termed and is stronger nucleophile.
Question 2
1 / -0

Which statement is true about S_N2 mechanism?

A
The rate of reaction increases on increasing strength of the nucleophile

B
The reaction is faster in polar aprotic solvents

C
The rate of reaction increases as the leaving group ability increases

D
Allof the above

Solution

Stronger the nucleophile, faster the S_N2 reaction. Polar aprotic solvent solvate cations, makes anionic nucleophile more available for reaction, hence faster reaction. A better leaving group lowers the activation energy increasing rate of S_N2 reaction.
Question 3
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A correct statement about transition state of S_N2 reaction is

A
the transition state proceeds and follow an unstable reaction intermediate

B
the transition state will always have net negative charge

C
existence of this state implies an exothermic reaction

D
the single transition state represents the point of maximum free energy of the reaction

Solution

S_N2 reaction is a one step (concerted) reaction that involes a single transition state.
Question 4
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What is the correct increasing order of reactivity of the followings in S_N2 reaction ?
I. CH₂ = CHCH₂ — Br
II. CH₂ = CH— I
III. CH₃CH₂CH₂ — I
IV. CH₃OCH₂CH₂ — I

A
I < II < III < IV

B
III < II < I < IV

C
II < III < IV < I

D
II < I < III < IV

Solution

Allyl bromide (I) is most reactive among the given halides as pi bonds from allylic position stabilises the transition state. Vinyl iodide (II) is least reactive due to partial double bond character. Electron withdrawing inductive effect of CH₃O^- increases reactivity of (IV) over (III)
Question 5
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What is the correct increasing order of reactivity of the following in the S_N2 reaction?

A
I < II < III < IV

B
III < II < I < IV

C
II < III < IV < I

D
Ill < I < II < I V

Solution

(IV) is most reactive as it is benzylic as well as electron withdrawing effect of — NO₂ further increases the reactivity. (Ill) is least reactive due to resonance effect resulting in partial double bond character between carbon and chlorine. (I) is less reactive in S_N2 reaction than II, due to greater steric hindrance in (I).
Question 6
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Consider the two lines shown in the diagram given below.
Q.
In a S_N2 reaction, these two lines compare the effect of the

A
substrate

B
nucleophile

C
leaving group

D
substrate or nucleophile

Solution

Substrates are same as they are at same potential energies. Nucleophiles are different as magnifested by different activation energies and different products with different potential energies,
Question 7
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Consider the two lines shown in the diagram given below.
Q.
Which of the following apply appropriately to a S_N2 reaction?

A
Graph I could represent Cl^- and Graph II represents I^- leaving group

B
Graph I could represent HO^- and Graph II represents CH₃COO^- nucleophile

C
Graph I could represent H₂O and Graph II H₂S as nucleophile

D
Graph I could represent (CH₃)₂NH and Graph II to (CH₃)₂N^- nucleophiles

Solution

HO^-is stronger nucleophile than CH₃COO^- . Hence, lower activation energy of (I) than (II).
Question 8
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The correct statement concerning a S_N2 reaction is

A
the reaction mechanism involve atleast one reactive intermediate

B
transition state is pentavalent

C
product is formed after passing through several transition states

D
nucleophile attacks from front side on which leaving group is present

Solution

The transition state in S_N2 reaction is pentavalent as indicated here.