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Test: SN1 Reactions - NEET MCQ


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30 Questions MCQ Test - Test: SN1 Reactions

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Test: SN1 Reactions - Question 1

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

Detailed Solution for Test: SN1 Reactions - Question 1

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.

Test: SN1 Reactions - Question 2

In SN1 reaction, racemisation occurs if the reaction occurs at a stereogenic centre, however, 50:50 mixture of enantiomers are rarely obtained, why?

Detailed Solution for Test: SN1 Reactions - Question 2

In SN1 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.

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Test: SN1 Reactions - Question 3

Pick out the most reactive alkyl halide for an SN1 reaction.

Detailed Solution for Test: SN1 Reactions - Question 3

Tertiary halide would be most reactive in SN1 reaction.

Test: SN1 Reactions - Question 4

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

Detailed Solution for Test: SN1 Reactions - Question 4

Tertiary halide would react at fastest rate with AgNO3 as reaction will proceed by SN1 mechanism.

Test: SN1 Reactions - Question 5

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

Detailed Solution for Test: SN1 Reactions - Question 5

Y forms a tertiary carbocation which rearranges to a further more stable benzylic carbocation.

Test: SN1 Reactions - Question 6

Which of the following statement(s) is/are true for SN1 reaction?

I. The rate of SN1 reaction depends on concentration of alkyl halide
II. The rate of SN1 reaction depends on concentration of nucleophile
III. SN1 reactions of alkyl halides are favoured by non-polar solvents

Detailed Solution for Test: SN1 Reactions - Question 6

Rate of SN1 reaction is directly proportional to concentration of alkyl halide but independent of concentration of nucleophile. Non-polar solvents play no role in SN1 reaction.

Test: SN1 Reactions - Question 7

From the following, pick out the potential energy profile for a SN1 reaction.

Detailed Solution for Test: SN1 Reactions - Question 7

SN1 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 SN1 reaction

Test: SN1 Reactions - Question 8

The most and least reactive electrophiles respectively in a SN1 reaction are


Detailed Solution for Test: SN1 Reactions - Question 8

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 SN1 reaction

Test: SN1 Reactions - Question 9

Pick out the strongest substrate(s) for a SN1 reaction.

Detailed Solution for Test: SN1 Reactions - Question 9

It forms a secondary carbocation which, by hydride shift, rearranges to a tertiary carbocation.

Test: SN1 Reactions - Question 10

Pick out the following factor(s) which promote a SN1 reaction :

I. Temperature
II. Concentration of nucleophile
III. Concentration of alkyl halide
IV. Aprotic solvents

Detailed Solution for Test: SN1 Reactions - Question 10

Increasing temperature increases rate of any reaction. Also, rate of SN1 reaction is directly proportional to concentration of alkyl halide but independent of nucleophile and aprotic solvent.

Test: SN1 Reactions - Question 11

Which of the following alkyl halides is respectively most and least electrophilic in SN1 reaction?

Detailed Solution for Test: SN1 Reactions - Question 11

(III) forms tertiary carbocation, hence most reactive. (I) is least reactive as highly unstable carbocation is formed at bridge head carbon of bicyclic compound.

Test: SN1 Reactions - Question 12

Which of the following is true regarding a SN1 reaction?

Detailed Solution for Test: SN1 Reactions - Question 12

Protic solvents solvate carbocation, promotes SN1 reaction.

Test: SN1 Reactions - Question 13

Rank the following molecules increasing in order of relative rate of SN1 solvolysis with methanol and heat.

Detailed Solution for Test: SN1 Reactions - Question 13

(V) form s m ost stable, tertiary allylic, carbocation. (II) is vinylic halide, least reactive.

Test: SN1 Reactions - Question 14

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

Detailed Solution for Test: SN1 Reactions - Question 14


Test: SN1 Reactions - Question 15

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

Detailed Solution for Test: SN1 Reactions - Question 15

(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.

Test: SN1 Reactions - Question 16

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.

Detailed Solution for Test: SN1 Reactions - Question 16

(II) forms more stable carbocation than (I).

Test: SN1 Reactions - Question 17

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.

Detailed Solution for Test: SN1 Reactions - Question 17

Both statements are true but the two different products are due to resonance in carbocation intermediate as

*Multiple options can be correct
Test: SN1 Reactions - Question 18

One or More than One Options Correct Type

Direction (Q. Nos. 18-22) This section contains 5 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 SN1 reaction?

Detailed Solution for Test: SN1 Reactions - Question 18

H2O has higher solvating power than CH3CH2OH,hence faster SN1 reaction occur in H2O. Reaction proceeds via carbocation intermediate, it passes through more than one transition states. Due to the presence of some intimate ion pair, SN1 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 CH318OH and CH3OH.

*Multiple options can be correct
Test: SN1 Reactions - Question 19

When the reactants shown below undergo substitution, which of the products will form?

Detailed Solution for Test: SN1 Reactions - Question 19



(I) gives (a) and (b) while (II) gives (c) and (d).

*Multiple options can be correct
Test: SN1 Reactions - Question 20

If a pure dextrorotatory enantiomer of the substrate of the following reaction is boiled with water, the correct statement(s) regarding SN1 product(s) is/are

Detailed Solution for Test: SN1 Reactions - Question 20

SN1 reaction takes place giving partial racemisation but net inversion of configuration at chiral α-carbon.

*Multiple options can be correct
Test: SN1 Reactions - Question 21

What is/are the expected solvolysis product(s) in the following reaction?

Detailed Solution for Test: SN1 Reactions - Question 21


*Multiple options can be correct
Test: SN1 Reactions - Question 22

Which of the following can catalyse the following SN1 reaction?

Detailed Solution for Test: SN1 Reactions - Question 22

ZnCI2 is a Lewis acid, helps in formation of carbocation. AgNO3 form s AgCI precipitate, derive heterolysis reaction belo w in forward direction:

From the given information structure of A can be derived as:

Test: SN1 Reactions - Question 23

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 SN1 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 CH2 group 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 SN1 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?

Detailed Solution for Test: SN1 Reactions - Question 23

It shows geometrical isomerism as well as it has a chiral carbon. Hence, A will have four stereoisomers

Test: SN1 Reactions - Question 24

A chemist isolated a compound A with molecular formula C7H13Br. A undergoes very fast SN1 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 CH2 group 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 SN1 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 ?

Detailed Solution for Test: SN1 Reactions - Question 24

 Alcohols B and C are: 


Both S and C have one chiral carbon each, both show optical isomerism.

Test: SN1 Reactions - Question 25

A chemist isolated a compound A with molecular formula C7H13Br. A undergoes very fast SN1 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 CH2 group 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 SN1 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?

Detailed Solution for Test: SN1 Reactions - Question 25

It has three chiral carbon, hence eight stereoisomers.

Test: SN1 Reactions - Question 26

A chemist isolated a compound A with molecular formula C7H13Br. A undergoes very fast SN1 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 CH2 group 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 SN1 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 ?

Detailed Solution for Test: SN1 Reactions - Question 26

Test: SN1 Reactions - Question 27

A chemist isolated a compound A with molecular formula C7H13Br. A undergoes very fast SN1 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 CH2 group 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 SN1 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?

Detailed Solution for Test: SN1 Reactions - Question 27

*Answer can only contain numeric values
Test: SN1 Reactions - Question 28

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 SN1 reaction?


Detailed Solution for Test: SN1 Reactions - Question 28



*Answer can only contain numeric values
Test: SN1 Reactions - Question 29

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




Detailed Solution for Test: SN1 Reactions - Question 29

Only (iii), (iv), (v), (vi) and (viii) form carbocations more stable than benzyl carbocation.

*Answer can only contain numeric values
Test: SN1 Reactions - Question 30

Following compound when heated in ethanol, SN1 reaction occur involving rearrangement of carbocation.

Q. 

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


Detailed Solution for Test: SN1 Reactions - Question 30

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