Test: SN1 Reactions


30 Questions MCQ Test Chemistry Class 12 | Test: SN1 Reactions


Description
This mock test of Test: SN1 Reactions for Class 12 helps you for every Class 12 entrance exam. This contains 30 Multiple Choice Questions for Class 12 Test: SN1 Reactions (mcq) to study with solutions a complete question bank. The solved questions answers in this Test: SN1 Reactions quiz give you a good mix of easy questions and tough questions. Class 12 students definitely take this Test: SN1 Reactions exercise for a better result in the exam. You can find other Test: SN1 Reactions extra questions, long questions & short questions for Class 12 on EduRev as well by searching above.
QUESTION: 1

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

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

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

Solution:

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.

QUESTION: 3

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

Solution:

Tertiary halide would be most reactive in SN1 reaction.

QUESTION: 4

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

Solution:

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

QUESTION: 5

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

Solution:

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

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

Solution:

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.

QUESTION: 7

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

Solution:

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

QUESTION: 8

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


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 SN1 reaction

QUESTION: 9

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

Solution:

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

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

Solution:

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.

QUESTION: 11

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

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

Which of the following is true regarding a SN1 reaction?

Solution:

Protic solvents solvate carbocation, promotes SN1 reaction.

QUESTION: 13

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

Solution:

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

QUESTION: 14

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

Solution:


QUESTION: 15

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

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

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.

Solution:

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

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.

Solution:

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

*Multiple options can be correct
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?

Solution:

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
QUESTION: 19

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

Solution:



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

*Multiple options can be correct
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

Solution:

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

*Multiple options can be correct
QUESTION: 21

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

Solution:


*Multiple options can be correct
QUESTION: 22

Which of the following can catalyse the following SN1 reaction?

Solution:

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:

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?

Solution:

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

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 ?

Solution:

 Alcohols B and C are: 


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

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?

Solution:

It has three chiral carbon, hence eight stereoisomers.

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 ?

Solution:

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?

Solution:

*Answer can only contain numeric values
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?


Solution:



*Answer can only contain numeric values
QUESTION: 29

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




Solution:

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

*Answer can only contain numeric values
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?


Solution: