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Haloalkanes and Haloarenes Test - 10

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Haloalkanes and Haloarenes Test - 10

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Question 1
4 / -1

The atom which defines the structure of a family of organic compounds and their properties is called ___________

A
Resonating structure

B
Homologous structure

C
Functional group

D
Nucleophile

Solution

Explanation: The atom which defines the structure of a family of organic compounds and their properties is called a functional group. Functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules.
Question 2
4 / -1

In S_N1 reaction, racemisation occurs if the reaction occurs at a stereogenic centre, however, 50:50 mixture of enantiomers are rarely obtained, why?

A
Usually one enantiomer is more stable than other

B
Retention of configuration is always favoured in reaction

C
Hydroxylic solvent favour retention of configuration

D
There is steric hindrance to the approach of nucleophile from the front side as some of the leaving group are not departed completely which favour inversion of configuration

Solution

In S_N1 reaction, some of the substrate, even after ionisation, remains associated as an intimate ion pair preventing nucleophilic attacks from front side and gives inverted product.

Due to partial reaction of nucleophile with intimate ion pair, net inversion of configuration is observed although predominant reaction occurs at planar carbocation giving racemic products.
Question 3
4 / -1

Pick out the most reactive alkyl halide for an S_N1 reaction.

A

B

C

D

Solution

Tertiary halide would be most reactive in S_N1 reaction.
Question 4
4 / -1

Pick out the compound which reacts fastest in the presence of AgNO₃.

A
(CH₃)₃CCI

B
(CH₃)₂CHCH₂CI

C
(CH₃)₂CHCI

D
CH₃CH₂CI

Solution

Tertiary halide would react at fastest rate with AgNO₃ as reaction will proceed by S_N1 mechanism.
Question 5
4 / -1

From the following, pick out the explanation for why molecule Y hydrolyses faster than molecule Z.

A
Less steric hindrance

B
Neighbouring group participation

C
Greater carbocation stability

D
Better solvent

Solution

Y forms a tertiary carbocation which rearranges to a further more stable benzylic carbocation.
Question 6
4 / -1

Which of the following statement(s) is/are true for S_N1 reaction?
I. The rate of S_N1 reaction depends on concentration of alkyl halide
II. The rate of S_N1 reaction depends on concentration of nucleophile
III. S_N1 reactions of alkyl halides are favoured by non-polar solvents

A
Only I

B
Only II

C
Only III

D
Both I and III

Solution

Rate of S_N1 reaction is directly proportional to concentration of alkyl halide but independent of concentration of nucleophile. Non-polar solvents play no role in S_N1 reaction.
Question 7
4 / -1

From the following, pick out the potential energy profile for a S_N1 reaction.

A

B

C

D

Solution

S_N1 reaction proceeds via carbocation intermediate which is being indicated here by two transition states and a small trough between reactant and product. Also the second transition state must be below first transition state in S_N1 reaction
Question 8
4 / -1

The most and least reactive electrophiles respectively in a S_N1 reaction are

A
Both I and.II

B
Both II and III

C
Both I and III

D
Both III and IV

Solution

Electron donating —CH₃ gro up stabilises benzylic carbocation, hence increases reactivity of corresponding substrate. Electron withdrawing —NO₂ decreases stability of carbocation, decreases reactivity of corresponding substrate in S_N1 reaction
Question 9
4 / -1

Pick out the strongest substrate(s) for a S_N1 reaction.

A
Only I

B
Only II

C
Only III

D
Only IV

Solution

It forms a secondary carbocation which, by hydride shift, rearranges to a tertiary carbocation.
Question 10
4 / -1

Pick out the following factor(s) which promote a S_N1 reaction :
I. Temperature
II. Concentration of nucleophile
III. Concentration of alkyl halide
IV. Aprotic solvents

A
Both I and II

B
Both II and III

C
Both III and IV

D
Both I and III

Solution

Increasing temperature increases rate of any reaction. Also, rate of S_N1 reaction is directly proportional to concentration of alkyl halide but independent of nucleophile and aprotic solvent.
Question 11
4 / -1

Which of the following alkyl halides is respectively most and least electrophilic in S_N1 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 12
4 / -1

Which of the following is true regarding a S_N1 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_N1 reaction.
Question 13
4 / -1

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 14
4 / -1

Which is the most likely product when the following iodide is heated with water?

A

B

C

D

Solution
Question 15
4 / -1

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 16
4 / -1

Statement Type
Direction (Q. Nos. 16 and 17) 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 17
4 / -1

Statement I : When 3-bromo propene, which contain a labelled ¹³C 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 18
4 / -1

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
All of 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 19
4 / -1

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 20
4 / -1

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.
Question 21
4 / -1

The chloro compound which can be used as fire extinguisher is:

A
CH₃Cl

B
COCl₂

C
CCl₄

D
CHCl₃

Solution

The correct answer is Option C.

Its use in the home as a spot remover should be avoided because of its poisonous nature.
Because it's vapours (incombustible vapours) are denser than air which leads to a smoother flame.
Question 22
4 / -1

Exposure to lower levels of a compound in air can lead to slightly impaired hearing and vision. Identify the compound.

A
Chloroform

B
Chloromethane

C
Carbon tetrachloride

D
Methylene chloride

Solution

The correct answer is Option D.

Methylene chloride (Dichloromethane) Dichloromethane, also known as methylene chloride, is one of the polyhalogen compounds present in the form of solvent. Low levels of methylene chloride exposure in the air can cause slight hearing and vision impairment.
Question 23
4 / -1

Comprehension Type
Direction (Q. Nos. 23-27) This section contains a paragraph, describing theory, experiments, data, etc.
Five questions related to the paragraph have been given. Each question has only one correct answer among the four given options (a), (b), (c) and (d).
Passage
A chemist isolated a compound A with molecular formula C₇H₁₃Br. A undergoes very fast S_N1 reaction. Spectroscopic evidence indicated that compound A has the following structural characteristics : It contains five sp³-hybridised carbon atoms. Among those five sp³ carbon atoms, three are methyl groups, one CH₂group and one CH group.
It also contains two sp²-hybridised carbon atoms. Also there is only one hydrogen atom attached to sp² carbons.
The compound contains a total of six aliylic hydrogen atoms.
The carbon atom that holds the Br has one H attached to it.
Working Space
When compound A reacts with boiling water, it undergoes a S_N1 reaction and produces two principal products B and C. Both B and C are alcohols with their molecular formula C₇H₁₄O. Among the two alcohols, B has the —OH group attached to a sp³ carbon atom that has no H -atoms bonded to it.
Q.
How many stereoisomers are possible for A?

A
2

B
3

C
4

D
None of these

Solution

It shows geometrical isomerism as well as it has a chiral carbon. Hence, A will have four stereoisomers
Question 24
4 / -1

A chemist isolated a compound A with molecular formula C₇H₁₃Br. A undergoes very fast S_N1 reaction. Spectroscopic evidence indicated that compound A has the following structural characteristics : It contains five sp³-hybridised carbon atoms. Among those five sp³ carbon atoms, three are methyl groups, one CH₂group and one CH group.
It also contains two sp²-hybridised carbon atoms. Also there is only one hydrogen atom attached to sp² carbons.
The compound contains a total of six aliylic hydrogen atoms.
The carbon atom that holds the Br has one H attached to it.
Working Space
When compound A reacts with boiling water, it undergoes a S_N1 reaction and produces two principal products B and C. Both B and C are alcohols with their molecular formula C₇H₁₄O. Among the two alcohols, B has the —OH group attached to a sp³ carbon atom that has no H -atoms bonded to it.
Q.
What can be said about the isomerism shown by the two alcohols B and C ?

A
Both B and C show stereoisomerism and can be resolved into enantiomers

B
B and C are stereoisomers

C
Both B and C show stereoisomerism but only C can be resolved into enantiomers

D
Neither B nor C can be resolved into enantiomers

Solution

Alcohols B and C are:

Both S and C have one chiral carbon each, both show optical isomerism.
Question 25
4 / -1

A chemist isolated a compound A with molecular formula C₇H₁₃Br. A undergoes very fast S_N1 reaction. Spectroscopic evidence indicated that compound A has the following structural characteristics : It contains five sp³-hybridised carbon atoms. Among those five sp³ carbon atoms, three are methyl groups, one CH₂group and one CH group.
It also contains two sp²-hybridised carbon atoms. Also there is only one hydrogen atom attached to sp² carbons.
The compound contains a total of six aliylic hydrogen atoms.
The carbon atom that holds the Br has one H attached to it.
Working Space
When compound A reacts with boiling water, it undergoes a S_N1 reaction and produces two principal products B and C. Both B and C are alcohols with their molecular formula C₇H₁₄O. Among the two alcohols, B has the —OH group attached to a sp³ carbon atom that has no H -atoms bonded to it.
Q.
If the starting compound A is brominated in gas phase in the presence of a Lewis acid catalyst, a tribromide would result from addition of Br₂ to . How many different structures of stereoisomers can be drawn for this tribromide?

A
2

B
4

C
8

D
None of these

Solution

It has three chiral carbon, hence eight stereoisomers.
Question 26
4 / -1

A chemist isolated a compound A with molecular formula C₇H₁₃Br. A undergoes very fast S_N1 reaction. Spectroscopic evidence indicated that compound A has the following structural characteristics : It contains five sp³-hybridised carbon atoms. Among those five sp³ carbon atoms, three are methyl groups, one CH₂group and one CH group.
It also contains two sp²-hybridised carbon atoms. Also there is only one hydrogen atom attached to sp² carbons.
The compound contains a total of six aliylic hydrogen atoms.
The carbon atom that holds the Br has one H attached to it.
Working Space
When compound A reacts with boiling water, it undergoes a S_N1 reaction and produces two principal products B and C. Both B and C are alcohols with their molecular formula C₇H₁₄O. Among the two alcohols, B has the —OH group attached to a sp³ carbon atom that has no H -atoms bonded to it.
Q.
If the original compound A is treated with LiAIH₄ a new compound D(C₇H₁₄) would be produced. How many different structure(s) can be drawn for this D ?

A
1

B
2

C
3

D
4

Solution
Question 27
4 / -1

A chemist isolated a compound A with molecular formula C₇H₁₃Br. A undergoes very fast S_N1 reaction. Spectroscopic evidence indicated that compound A has the following structural characteristics : It contains five sp³-hybridised carbon atoms. Among those five sp³ carbon atoms, three are methyl groups, one CH₂group and one CH group.
It also contains two sp²-hybridised carbon atoms. Also there is only one hydrogen atom attached to sp² carbons.
The compound contains a total of six aliylic hydrogen atoms.
The carbon atom that holds the Br has one H attached to it.
Working Space
When compound A reacts with boiling water, it undergoes a S_N1 reaction and produces two principal products B and C. Both B and C are alcohols with their molecular formula C₇H₁₄O. Among the two alcohols, B has the —OH group attached to a sp³ carbon atom that has no H -atoms bonded to it.
Q.
If the starting compound A is treated with ethanolic solution of KOH in boiling condition, a further new compound E (C₇H₁₂) is produced as major product by E2 elimination reaction. Which of the following statement will be consistent with E?

A
It will have no stereogenic centre i.e. it will not show stereoisomerism

B
It will show stereoisomerism but cannot be resolved into enantiomers

C
It will have more than one stereogenic centres and more than two, different structures of stereoisomers can be drawn for E

D
None of the above appropriately applies to E

Solution
Question 28
4 / -1

One Integer Value Correct Type

Direction (Q. Nos. 28-30) This section contains 3 questions. When worked out will result in an integer from 0 to 9 (both inclusive).

Consider the following solvolysis reaction.

Q.

How many principal products would be formed by S_N1 reaction?

A
6

B
7

C
8

D
9

Solution
Question 29
4 / -1

How many of the following undergo solvolysis reaction faster than benzyl chloride?

A
1

B
2

C
5

D
4

Solution

Only (iii), (iv), (v), (vi) and (viii) form carbocations more stable than benzyl carbocation.
Question 30
4 / -1

Following compound when heated in ethanol, S_N1 reaction occur involving rearrangement of carbocation.

Q.

In the major product, how many carbon atoms are present in the single largest ring?

A
4

B
5

C
7

D
6

Solution

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