Reaction Mechanism MCQs [Organic Chemistry]

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


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


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


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


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


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



Kinetics of SN2 reactions are normally  _____ .

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

Question’s Answer: Second order



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


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


Which of the carbocation is likely stable?

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

Question’s Answer: CH2=CH-CH2


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


Which is an electrophile?

  1. SO2
  2. NF3
  3. SO3
  4. BF3

Question’s Answer: SO3


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


Free radicals are characterized by which of the following?

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

Question’s Answer: Paramagnetism


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


Entropy is a measure of

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

Question’s Answer: Randomness



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

  1. E2
  2. E1
  3. SN2
  4. SN1

Question’s Answer: E1


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


Which reactions are not shown by benzaldehyde?

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

Question’s Answer: Beckmann rearrangement


SN2 reactions are

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

Question’s Answer: Bimolecular


Cannizzaro reaction involves migration of which species

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

Question’s Answer: Hydride ion


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


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


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


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


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


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


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



The SN2 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


Which statements about the SN1 mechanism is false?

  1. SN1 reactions are unimolecular
  2. The SN1 mechanism involves a single step
  3. SN1 reactions are first order
  4. SN1 reactions usually occur in two steps

Question’s Answer: The SN1 mechanism involves a single step


Which is the most reactive compound by the SN2 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


Which is the most reactive compound by the SN1 mechanism?

  1. CH3CH2CH2Br
  2. CH2=CHCH2Br
  3. Both A & B are equally reactive
  4. None of A, B, and C can undergo SN1

Question’s Answer: CH2=CHCH2Br


Which statements is false?

  1. SN1 reactions undergo partial inversion of configuration
  2. SN2 reactions undergo partial inversion of configuration
  3. Both a & b
  4. None of the above

Question’s Answer: SN1 reactions undergo partial inversion of configuration


Which is most reactive as a nucleophile?

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

Question’s Answer: CH3CH2O.


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


In most of the cases,_________ compete with SN2 reactions.

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

Question’s Answer: E2 Reactions


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


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


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


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


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


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


Which type of solvent needed for the reactions to perform SN2 mechanism.

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

Question’s Answer: Polar aprotic


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


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


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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