Reaction Mechanism MCQs [Organic Chemistry]

By: Prof. Dr. Fazal Rehman | Last updated: February 3, 2024

MCQs based on questions and answers on Reaction Mechanism in organic chemistry.

Amongst the following which will show anti-Markownikoff addition in the absence of peroxides

1. CH₂=CH-CF₃
2. CH₂=CH-CH₃
3. CH₂=CH-CI
4. None of A, B, and C

Question’s Answer: CH₂=CH-CF₃

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According to transition state theory which is not the compulsory requirement for reaction to occur

1. Energy of activation
2. Collision
3. Transition state
4. All of A,B, and C

Question’s Answer: Collision

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With reference to collision theory, reaction takes place when molecules are ________.

1. Collidingb
2. In proper orientation
3. Activated
4. All of A,B, and C

Question’s Answer: All of A,B, and C

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Which is an example of sigmatropic rearrangement?

1. Claisen rearrangement
2. Diels-Alder reaction
3. Hofmann bromamide reaction
4. Benzidine rearrangement

Question’s Answer: Claisen rearrangement

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Formation of polyamide ‘Nylon’ from adipic acid and hexamethylene diamine is an example of

1. Condensation reaction
2. Addition polymerisation
3. Copolymerisation
4. Condensation polymerization

Question’s Answer: Condensation polymerization

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Homolytic fission of covalent bond results in the formation of  ____ .

1. Carbocations
2. Free radicals
3. Carbanions
4. Both B. and C.

Question’s Answer: Free radicals

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Kinetics of S_N2 reactions are normally  _____ .

1. Pseudo-second
2. First order
3. Second order
4. None of A, B, and C

Question’s Answer: Second order

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Which is true about carbanions?

1. Carbanion carbon is sp³ hybridised
2. It has tetrahedral shape.
3. It has trigonal
4. Their order of stability is Pr. < Sec. <Ter.

Question’s Answer: Carbanion carbon is sp³ hybridised

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The order of stability of free radicals

[I] CH₂=CH-CH₂, [II] CH3CH₂, [III] (CH₃)₂CH and [IV] (CH₃)₃C is

1. I<II<III<IV
2. IV< III<II<I
3. II<I<III<IV
4. II<III<IV<I

Question’s Answer: II<III<IV<I

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Which of the carbocation is likely stable?

3. CH₃.CH₂
4. CH₂=CH-CH₂
5. (CH₃)₂C
6. (CH₃)₂CH

Question’s Answer: CH₂=CH-CH₂

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A reaction intermediate having only six electrons in the outer orbit of carbon but charge on it, is called ________.

1. Carbocation
2. Carbene
3. Carbanion
4. Free radiocal

Question’s Answer: Carbene

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Which is an electrophile?

1. SO₂
2. NF₃
3. SO₃
4. BF₃

Question’s Answer: SO₃

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Which is the reaction in which bond breaking and making processes take place simultaneously?

1. Synchronous reaction
2. No mechanism reaction
3. Free radical reaction
4. Multistep reaction

Question’s Answer: Synchronous reaction

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Free radicals are characterized by which of the following?

1. Low reactivity
2. Diamagnetism
3. Loss of electrons
4. Paramagnetism

Question’s Answer: Paramagnetism

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Heterolysis of which bond is likely to fors carbanion?

1. C-CI
2. C-Mg
3. C-O
4. C-N

Question’s Answer: C-Mg

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Entropy is a measure of

1. Heat content
2. Free energy
3. Randomness
4. Enthalpy

Question’s Answer: Randomness

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Dehydration of alcohol in acidic conditions is an example of
___________ reaction

1. E₂
2. E₁
3. S_N2
4. S_N1

Question’s Answer: E₁

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What is the type of reaction exhibited by alkanes?

1. Depends on type of reagent
2. Electrophilic substitution
3. Nucloephilic substitution.
4. Free radical substitution

Question’s Answer: Free radical substitution

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Which reactions are not shown by benzaldehyde?

1. Beckmann rearrangement
2. Perkin reaction
3. Cannizzaro reaction
4. Benzoin condensation

Question’s Answer: Beckmann rearrangement

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S_N2 reactions are

1. Usually occur through unimolecular
2. Unimolecular
3. Bimolecular
4. None of A, B, and C

Question’s Answer: Bimolecular

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Cannizzaro reaction involves migration of which species

1. Proton
2. Hydride ion
3. Carbene
4. Carbanion

Question’s Answer: Hydride ion

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The reaction of benzene ring are mainly

1. Free radical substitution
2. Nucleophilic substitution
3. Electrophonic substitution
4. Nucleophilic addition

Question’s Answer: Electrophonic substitution

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Which is the reactions of carbonyl group?

1. Nucleophilic addition
2. Electrophilic additions
3. Free radical addition
4. Nucloephilic substitutions

Question’s Answer: Nucleophilic addition

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The change in the state of hybridization of carbon in the reaction R-CN→RCONH₂

1. sp³ to sp²
2. sp to sp²
3. sp to sp³
4. sp² to sp

Question’s Answer: sp to sp²

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Diels-Alder reaction is an example of which type of reaction

A: Electrophilic addition

1. Nucleophilic addition
2. Sigmatropic reaction
3. Pericyclic reaction

Question’s Answer: Pericyclic reaction

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In the thermal conversion of cyclobutene to butadiene, the reaction is symmetry allowed if there is

1. Conrotatory opening of the ring
2. No correlation of symmetry
3. Disrotatory opening of ring
4. Reaction does not occur

Question’s Answer: Conrotatory opening of the ring

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Which bond is likely to break by homolysis?

1. C-H
2. C-CI
3. H-CI
4. H-O

Question’s Answer: C-H

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Heterolysis of a ‘C-C’ covalent bond forms?

1. Free radicals
2. Carbanions only
3. Carbocations only
4. Both carbocations and carbanions

Question’s Answer: Both carbocations and carbanions

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The S_N2 mechanism occurs in _______.

1. Three step
2. One step
3. Depends upon nucleophile
4. None of A, B, and C

Question’s Answer: One step

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Which statements about the S_N1 mechanism is false?

1. S_N1 reactions are unimolecular
2. The S_N1 mechanism involves a single step
3. S_N1 reactions are first order
4. S_N1 reactions usually occur in two steps

Question’s Answer: The S_N1 mechanism involves a single step

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Which is the most reactive compound by the S_N2 mechanism?

1. (CH₃)₂CHCH2Br
2. CH₃CH₂CH₂CH2Br
3. Both A & B are equally reactive
4. None of A, B, and C can undergo SN2

Question’s Answer: CH₃CH₂CH₂CH2Br

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Which is the most reactive compound by the S_N1 mechanism?

1. CH₃CH₂CH₂Br
2. CH₂=CHCH2Br
3. Both A & B are equally reactive
4. None of A, B, and C can undergo S_N1

Question’s Answer: CH₂=CHCH2Br

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Which statements is false?

1. S_N1 reactions undergo partial inversion of configuration
2. S_N2 reactions undergo partial inversion of configuration
3. Both a & b
4. None of the above

Question’s Answer: S_N1 reactions undergo partial inversion of configuration

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Which is most reactive as a nucleophile?

1. PhO-
2. CH₃O.
3. CH₃NH₂.
4. CH₃CH₂O.

Question’s Answer: CH₃CH₂O.

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Which statements about the E₁ mechanism is false?

1. Reactions by the El mechanism are unimolecular in the rate-determining step
2. Reactions by the El mechanism are normally first order
3. Reactions by the El mechanism usually occur in two step
4. Reactions by the El mechanism are multi-step reactions

Question’s Answer: Reactions by the El mechanism are multi-step reactions

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In most of the cases,_________ compete with S_N2 reactions.

1. E₂ Reactions
2. E₁ Reactions
3. Both A and B
4. None of A, B, and C

Question’s Answer: E₂ Reactions

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Which statements about the E2 mechanism is false?

1. Reactions by the E2 mechanism usually occur in two steps
2. Reactions by the E2 mechanism are normally second order
3. Reactions by the E2 mechanism usually occur in one step
4. Reactions by the E2 mechanism are always bimolecular

Question’s Answer: Reactions by the E2 mechanism usually occur in two steps

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Which statements about mechanisms of elimination reaction is false?

1. The E1 mechanism does not require a base
2. The E2 mechanism normally occurs under highly basic conditions
3. The E2 mechanism is stereospecific
4. The El mechanism is usually unimolecular in the rate-determining step but leads to a second order rate law

Question’s Answer: The El mechanism is usually unimolecular in the rate-determining step but leads to a second order rate law

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Bromobenzene can’t undergo reaction due to which of the following?

1. Nucleophile is repelled by when it attacks on backside of SP² carbon
2. Phenyl groups is inductively electron donating
3. The E2 mechanism is stereospecific
4. Br has poor electron withdrawing effect

Question’s Answer: Nucleophile is repelled by when it attacks on backside of SP² carbon

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In elimination reactions bulky leaving groups prefers to give

1. Saytzeff product
2. Hoffmann product
3. Sometimes Saytzeff and sometimes Hoffmann product
4. None of A, B, and C

Question’s Answer: Hoffmann product

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In Saytzeff product a base nucleophile attacks the substrate

1. Large sized
2. Small sized
3. Small or large sized (size of base no matters)
4. None of A, B, and C

Question’s Answer: Small sized

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In elimination reactions, poor leaving group favors to follow which mechanism?

1. E1 mechanism
2. E2 mechanism
3. Both a & b are equally preferable
4. None of A, B, and C

Question’s Answer: E1 mechanism

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Which type of solvent needed for the reactions to perform S_N2 mechanism.

1. Polar aprotic
2. Non-polar
3. Polar protic
4. Aqueous

Question’s Answer: Polar aprotic

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Mechanism of reaction may be studied with the help of

1. Stereo chemical evidence
2. Isotopic labeling
3. Intermediate trapping
4. All of A,B, and C

Question’s Answer: All of A,B, and C

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In the dehydrohalogenation of 2-chlorobutane, what is the main product?

1. 2-Butanol
2. 1-Butanol
3. 1-Butene
4. 2-Butene

Question’s Answer: 2-Butene

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Carbene intermediate is involved in which reaction

1. Carbylamine reaction
2. Reimer-Tiemann
3. Both
4. None

Question’s Answer: Both

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