Haloalkanes & Haloarenes Test

Result

Haloalkanes & Haloarenes Test - 7

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Question 1
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Passage I

The following E2 is carried out with different halogen substituent:

From the percentage yield of two products observed with different leaving group, it was concluded that both ease of leaving group and steric hindrance to the approach of base CH₃ O^- to β-H affect the orientation of elimination reaction.

Q.

During formation of products in the given elimination reaction, the highest energy transition state would have been produced when methoxide ion reacts with

A
2-iodohexane to form 2-hexene

B
2-iodohexane to form 1-hexene

C
2-fluorohexane to form 1-hexene

D
2-fluorohexane to form 2-hexene

Solution

Fluorine is poorest leaving group and formation of 2-hexene involve greater steric hindrance hence, highest energy transition state,
Question 2
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Passage I

The following E2 is carried out with different halogen substituent:

From the percentage yield of two products observed with different leaving group, it was concluded that both ease of leaving group and steric hindrance to the approach of base CH₃ O^- to β-H affect the orientation of elimination reaction.

Q.

If we consider X to be iodine in the given elimination reaction, the number of different elimination products present in the flask-1 would be?

A
2

B
3

C
4

D
5

Solution
Question 3
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Passage I

The following E2 is carried out with different halogen substituent:

From the percentage yield of two products observed with different leaving group, it was concluded that both ease of leaving group and steric hindrance to the approach of base CH₃ O^- to β-H affect the orientation of elimination reaction.

Q.

Transition state with maximum double bond character will be formed when methoxide reacts with

A
2-iodohexane to form 2-hexene

B
2-iodohexane to form 1-hexene

C
2-fluorohexane to form 1-hexene

D
none

Solution

Iodine is best leaving group and 2-hexene is more substituted product, hence major product,
Question 4
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Passage I

The following E2 is carried out with different halogen substituent:

From the percentage yield of two products observed with different leaving group, it was concluded that both ease of leaving group and steric hindrance to the approach of base CH₃ O^- to β-H affect the orientation of elimination reaction.

Q.

Transition state with least double bond character will be formed when methoxide reacts with

A
2-iodohexane to form 2-hexene

B
2-iodohexane to form 1-hexene

C
2-fluorohexane to form 2-hexene

D
2-fluorohexane to form 1-hexene

Solution

It forms the highest energy transition state.
Question 5
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Passage II

When compound 1 is heated with C₂ H₅ ONa compound 2 and 3 are formed:

Two mechanisms were proposed for reaction I.
Mechanism A HBr is eliminated from compound 1 to form a symmetrical vinyl carbene intermediate A, which then rearranges to compound 2.

Mechanism B Ethoxide ion first abstract a proton to form a carbanion intermediate B which then rearranges with loss of bromide ion to form compound 2

To distinguish between the two machanisms, an isotopic labeling experiment was designed. Two compounds (Compound 4 and 5) were labelled with C-14 and each was treated separately with sodium ethoxide under identical experimental condition where following results were obtained.

Q.

Based on the results of scheme 1, the chemist most likely ruled out mechanism A because they assumed that intermediate A should have formed

A
compound 6 only

B
compound 7 only

C
equal amounts of 6 and 7

D
neither compound 6 nor 7

Solution
Question 6
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Passage II

When compound 1 is heated with C₂ H₅ ONa compound 2 and 3 are formed:

Two mechanisms were proposed for reaction I.
Mechanism A HBr is eliminated from compound 1 to form a symmetrical vinyl carbene intermediate A, which then rearranges to compound 2.

Mechanism B Ethoxide ion first abstract a proton to form a carbanion intermediate B which then rearranges with loss of bromide ion to form compound 2

To distinguish between the two machanisms, an isotopic labeling experiment was designed. Two compounds (Compound 4 and 5) were labelled with C-14 and each was treated separately with sodium ethoxide under identical experimental condition where following results were obtained.

Q.

Compound 2 and 6 can be distinguished from each other by all of the following techniques except:

A
gas chromatography

B
mass spectrometry

C
dipole moment measurement

D
polarimetry

Solution

2 and 6 are different compounds, can be separated by gas chromatography. They have different mass, can be distinguished by mass-spectrometry. 2 and 6 have different polarity, can be distinguished by dipole moment measurement. However both are achiral, cannot be distinguished by polarimetry.
Question 7
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Passage II

When compound 1 is heated with C₂ H₅ ONa compound 2 and 3 are formed:

Two mechanisms were proposed for reaction I.
Mechanism A HBr is eliminated from compound 1 to form a symmetrical vinyl carbene intermediate A, which then rearranges to compound 2.

Mechanism B Ethoxide ion first abstract a proton to form a carbanion intermediate B which then rearranges with loss of bromide ion to form compound 2

To distinguish between the two machanisms, an isotopic labeling experiment was designed. Two compounds (Compound 4 and 5) were labelled with C-14 and each was treated separately with sodium ethoxide under identical experimental condition where following results were obtained.

Q.

In reaction scheme 1, had the α-C to bromine be labelled with C-14

A
no change in observation regarding % of various products would have been observed

B
percentage of the compounds 6 and 7 formed from compound 4 would have been interchanged

C
percentage of the compounds 6 and 7 formed from compound 5 would have been interchanged

D
percentage of the compounds 6 and 7 formed from both compounds 4 and 5 would have been interchanged

Solution
Question 8
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Matching List Type

Direction : Choices for the correct combination of elements from Column I and Column II are given as options (a), (b), (c) and (d), out of which one is correct.

Q.

Match the reaction from Column I with the type of m echanism from Column II and mark the correct option from the codes given below.

A
a

B
b

C
c

D
d

Solution

(i) Given halide is a primary, predominantly undergo S_N 2 reaction.

(ii) Given halide is secondary, can undergo S_N 2 reaction. Also, E2 reaction leads to a conjugated system. Also it may react by E1 cb mechanism because it forms resonance stabilised carbanion.

(iii) It is a 3 °halide and in the presence of weak base H₂ O, weak nucleophile H₂ O , it may undergo unimolecular substitution (S_N 1) and elimination (E1) reaction.

(iv) It may form a stable benzylic carbocation after hydride shift, hence may react by S_N 1 mechanism. Also it is a secondary halide, may undergo S_N 2 reaction. It may also react by E2 reaction ai it gives conjugated system. Carbanion. formed at β-C will be stabilised by resonance from ring, hence may undergo E1 cb mechanism.
Question 9
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Match the alkyl halides in the Column I with the properties of their products produced in E2 elimination reaction in Column II and mark the correct option from the codes given below.

A
a

B
b

C
c

D
d

Solution
Question 10
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One Integer Value Correct Type

Direction : This section contains 2 questions. When worked out will result in an integer from 0 to 9 (both inclusive).

Q.

In the reaction given below how many elim ination products are formed in principle if reaction proceeds by E1 cb mechanism?

A
4

B
3

C
2

D
1

Solution
Question 11
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Consider the following reaction,

Q.

How many different stereoisomers of the major elimination product Y are possible?

A
1

B
2

C
3

D
0

Solution

The major elimination product is

Since, the diene above is symmetrical, only three geometrical isomers exist.