Haloalkanes and Haloarenes Test 14

Result

Haloalkanes and Haloarenes Test 14

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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 option is correct.
Q.
The incorrect statement concerning E1 reaction is

A
polar protic solvent increases reactivit

B
lewis acid catalyses reaction

C
reaction proceeds via carbocation intermediates

D
reaction proceeds via a single transition state

Solution

E1 Reactions involve carbocation intermediates which has characteristics of rearrangement into more stable carbocation, hence involves more than one transition states (usually).
Question 2
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The correct statement regarding a unimolecular elimination reaction is

A
Rearrangement of carbon skeleton may occur during elimination reaction

B
Reaction is stereospecific

C
If ¹⁴C replaces α-carbon of substrate, reactivity remains unaltered

D
In the given condition of E1 reaction, no substitution reaction takes place

Solution

E1 reaction proceeds via carbocation intermediate, rearrangement of carbon skeleton is very common in this reaction.
Question 3
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Consider the following reaction,

Q.
The correct statement concerning I and II is

A
I is the major product as it is formed at faster rate than II

B
II is the major product as it is formed at faster rate than I

C
I is major product as it is more stable than II

D
I and II are formed in comparable amounts

Solution

This is an example of E1 reaction and more substituted alkene (I) is formed as the major product.
Question 4
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Consider the following elimination reaction,
When reaction is carried out with C₂H₅ONain ethanol, 2-menthene is the major product while 3-menthene is the major product if reaction is substrate is heated in ethanol only. It is due to

A
with strong base, less substituted alkene is always the major product.

B
with strong base, reaction proceeds by E2 mechanism while with weak base, E1 reaction takes place.

C
methyl group gives steric hindrance to strong base in E2 reaction.

D
isopropyl group gives steric hindrance to strong base in E2 reaction.

Solution

With strong base C₂H₅ONa, reaction proceeds by E2 mechanism. Since, there is no H in the anti position at tertiary β-carbon, deprotonation occur from secondary β-carbon giving 2-menthene as the major product. On the other hand, with weak base, reaction proceeds by E1 mechanism and the most stable tertiary carbocation formed, gives the major product 3-menthene.
Question 5
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The reaction of tertiary butyl chloride in water to yield tertiary butyl alcohol is not appreciably affected by dissolved NaF; in DMSO, however, NaF bring about rapid formation of isobutene. It is because of

A
in DMSO, reaction predominates over S_N1

B
E₂ reaction is preferred over S_N1 in DMSO

C
E2 reaction is preferred over S_N2 in DMSO

D
fluoride ion is not solvated by DMSO

Solution

Polar aprotic solvents DMSO strongly favour E2 reaction giving isobutene product.
Question 6
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When (CH₃)₃C — Cl is heated in ethanol, both alkene and ether are formed simultaneously by E1 and S_N1 reaction. Which of the following will have adverse effect on both of the above reaction?

A
Presence of Lewis acid

B
Presence of some water in ethanol

C
Presence of some NaCI

D
Presence of some CHCI₃

Solution

Both S_N1 and E1 reaction involve formation of carbocation intermediate in slow rate determining step as :

Presence of NaCI derive the above reaction in backward direction by Le-Chatelier’s principle, hence has adverse effect on both E1 and S_N1 reaction.
Question 7
1 / -0

Consider the following reaction,

Q.
Increasing temperature increases the proportion of elimination (E1) product because

A
E1 product is enthalpy favoured

B
E1 product is entropy favoured

C
S_N1 product is entropy favoured

D
S_N1 product is enthalpy favoured

Solution

Reaction (II) leads to greater increase in entropy (Δn = 1). Hence, favoured at higher temperature due to greater decrease in ΔG than for reaction (I).
Question 8
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Which is the least reactive halide in both E₁ and S_N1 reaction?

A

B

C

D

Solution

Carbocation at bridge head carbon of bicyclic compound is highly unstable due to lack of planarity.