Named Reactions MCQ Quiz - Objective Question with Answer for Named Reactions - Download Free PDF

 

CONCEPT:

Knoevenagel Reaction

• The Knoevenagel reaction is a base-catalyzed condensation reaction between an aldehyde (or ketone) and a compound containing an active methylene group (such as diethyl malonate).
• It typically results in the formation of an α,β-unsaturated compound through the elimination of water.
• In this reaction, the base deprotonates the methylene group, forming a carbanion, which then attacks the carbonyl carbon of the aldehyde.

EXPLANATION:

• In the given reaction, benzaldehyde (C₆H₅CHO) reacts with diethyl malonate (CH₂(COOC₂H₅)₂) in the presence of a base.
• The reaction forms an α,β-unsaturated diester as the product, which is a characteristic product of the Knoevenagel condensation.
• The other options are incorrect:
  • Wittig reaction: Forms alkenes using phosphonium ylides, not applicable here.
  • Aldol condensation: Involves carbonyl compounds reacting with each other, not an active methylene compound.
  • Cannizzaro reaction: Occurs in aldehydes without alpha hydrogens and involves oxidation-reduction, not observed here.

Therefore, the correct answer is Option 1: Knoevenagel reaction.

CONCEPT:

Multi-step Reaction Mechanism: Buchwald–Hartwig Coupling, Heck Reaction, and Catalytic Hydrogenation

• This sequence involves three key transformations:
  1. Buchwald–Hartwig cross coupling: Pd-catalyzed C–N bond formation between aryl halide and amine.
  2. Heck reaction: Pd-catalyzed C–C coupling of an aryl halide with an alkene (β-eliminating the halide).
  3. Hydrogenation: Pd/C with H₂ reduces alkene double bonds (especially exocyclic ones) under mild conditions.
• Starting substrates:
  • 1-Iodo-2-phenylindole
  • Ethyl 4-bromobut-2-enoate

EXPLANATION:

• Step 1: The NH of indole couples with the brominated alkene ester via Pd(0) catalyst and base (K₂CO₃), forming a C–N bond.
• Step 2: Intramolecular Heck-type reaction occurs between the aryl iodide and the alkene of the side chain, forming a fused 5-membered ring (cyclization).
• Step 3: Hydrogenation (H₂, Pd/C in EtOH/AcOH) reduces the alkene in the fused ring (double bond becomes single).
• The product retains the ester group (COOEt), and forms a tetrahydrocarbazole framework fused with a 6-membered ring and an ethyl ester side chain.

Therefore, the major product formed is Option 2: a hydrogenated carbazole derivative with an ethyl ester group.

Concept:

Hydroboration-Oxidation Reaction

• The hydroboration-oxidation reaction involves the addition of diborane (B₂H₆) to an alkene, where the boron atom attaches to the less substituted carbon (anti-Markovnikov addition). This is followed by oxidation with alkaline hydrogen peroxide (H₂O₂), leading to the formation of an alcohol.
• The subsequent oxidation with hydrogen peroxide replaces the boron atom with a hydroxyl group (-OH), forming a product that retains the stereochemistry of the original alkene.

Explanation:

(These are the right products.)

Therefore, the correct product of the reaction is cis-2-Methylcyclohexanol (according to official answer key).

Concept:

Matching Organic Reactions with Their Corresponding Names

• Reaction (a): "Carbonyl compounds react with ylide to form alkene"
  • This reaction corresponds to the Wittig Reaction (iii), which involves the reaction of an aldehyde or ketone with a phosphorus ylide to form an alkene.
• Reaction (b): "Ketone reacts with zinc-mercury amalgam in HCl as reducing agent to form alkane"
  • This is a Clemmenesen Reduction (ii), a reduction of ketones to alkanes using zinc-mercury amalgam in the presence of hydrochloric acid.
• Reaction (c): "Carbonyl compounds react with basic solution of hydrazine as reducing agent to produce alkane"
  • This corresponds to the Wolff-Kishner Reduction (iv), which is used to reduce carbonyl compounds to alkanes using hydrazine and a base.
• Reaction (d): "Formaldehyde reacts with NaOH to form methanol"
  • This is an example of the Cannizzaro Reaction (i), which occurs when non-enolizable aldehydes, such as formaldehyde, react with a strong base to yield methanol and a carboxylate anion.

Correct Answer:

• Matching: (a) → (iii), (b) → (ii), (c) → (iv), (d) → (i)

Concept:

• The Pinacol-Pinacolone rearrangement is an organic reaction involving the acid-catalyzed rearrangement of a vicinal diol (a molecule with two hydroxyl groups on adjacent carbons) to a ketone or aldehyde.
• In this reaction, a molecule known as pinacol (or any similar vicinal diol) undergoes dehydration in the presence of an acid, leading to the formation of a carbocation intermediate. This carbocation then rearranges, and water is lost to form a pinacolone (or a similar ketone/aldehyde).

Explanation:

Therefore, the correct option is 4.

Concept:-

• The Aldar-ene reaction or ene reaction is a chemical reaction that involves an alkene with an allylic hydrogen (ene reaction) and enophile (a compound containing a multiple bond) to form a new σ-bond with the migration of the ene double bond and 1,5 hydrogen shift. 
• The mechanism of the following reaction is given below:

Explanation:-

• The mechanism of the reaction is shown below:

• From the above reaction, we can see that in the first step of the reaction Ti(OⁱPr)₄ acts as a lewis acid and forms complex with the oxygen atom of the more electrophilic aldehyde functional group of the substrate.
• In the next step, the complex undergoes an ene reaction with the diene.

Conclusion:-

Hence, the major product formed in the following reaction is

Concept:

• Diels-Alder reaction is a type of pericyclic reaction between an alkene (called dienophile) and a diene. 
• The reaction proceeds through concerted mechanism.
• It is a syn cycloaddition reaction and thus 'locked 'cis isomer favors the reactivity with dienophile.

Explanation:

Out of A and B, Compound A is less stable and more reactive. The higher reactivity towards the dienophile can be explained by following reason

• Compound A has smaller ring and thus it acts as more rigid cis diene. While compound B is 7-membered aromatic ring. Bigger rings are more flexible. Therefore, compound B will have lower reactivity towards the dienophile.

Compound A is reactive, the activation energy will be lower for the formation of P_A.

Conclusion:

Therefore, the correct energy profile of given reactions is:

Concept:

• Grubbs catalysts are Ruthenium containing Metal-carbene complexes, named after Robert H. Grubbs
• These complexes are used in olefin metathesis reactions, also known as Grubbs reaction.
• Metathesis reaction between 2 olefins involves formation of 4 membered ring, followed by rearrangement of the bond to get new olefinic bond.

Explanation:

• In the first step, the Grubbs catalyst exchange the groups  and form carbene with ethylene molecule           
• In the next step, the Ru-olefin carbene complex undergoes [2+2] cycloaddition reaction with the double bond present in given substrate      
• Further, 4 membered ring containing Ru will undergo rearrangement leading to ring opening. The Ru=C bond  again shows cycloaddition with another ethylene molecule to give 4 membered ring followed by rearrangement and ring opening to get double bonds with different substituents. 
•            
• Finally, there will be Sigmatropic rearrangement.        

Conclusion:

Therefore, the final product of given Grubbs reaction is :

Concept:

• Prins reaction is nucleophillic addition of alkene to aldehyde or ketone assisted by an acid
• intramolecular Prins reaction leads to cyclization and thus called Prins cyclization.
• Pinacole arrangement involves conversion of 1,2 diol system to carbonyl system in the presence of an acid (lewis acid or proton ).

Explanation:

• Firstly, SnCl4 (lewis acid) coordinates with oxygen whose lone pairs are  most available for donation.
• The positive charge on O coordinated to lewis acid will undergo neutralization by bond breaking and oxonium ion forms.
• In the next step, alkene adds to carbonyl carbon to form a 6-membered ring with a tertiary carbocation. This is called prins cyclization.
• Further, the formed carbocation undergoes pincaole rearrangement to give 5-membered ring

Conclusion:

The sequence of steps involved in the given chemical reaction are:

(1) formation of oxonium ion, (2) Prins cyclization and finally (3) Pinacole rearrangement.

Concept:

Reformastsky reaction:

• It is the preparation of β hydroxy esters by the reaction of a reactive organic halide such as α halo esters or its vinylog with a carbonyl compound in the presence of zinc Metal and subsequent hydrolysis.
• Solvents used are benzene, toluene, THF, etc.
• The aldehyde may be aliphatic, aromatic, heterocyclic and may contain substituents. 
• The substituents are generally unaffected. Reformatsky reaction is closely related to the Grignard reaction.
• The general mechanism involves the formation of intermediate ZnBrCH₂COOEt, which is analogous to RMgX.
• The organozinc compounds are less reactive than Grignard reagents and do not react with their own esteric group.
• The reactivity order of halo esters is iodo > chloro > Bromo.
• Besides aldehydes, methyl ketones and cyclic ketones, nitriles also gives Reformatsky reaction.

Explanation:

• In the first step, the zinc and α Bromo ester react to form the organozinc intermediate.
• The zinc salt then adds with the carbonyl group of the aldehyde or ketone.
• Subsequent hydrolysis gives the β keto ester.
• The reaction proceeds as follows:

​

Hence, the major product formed is:

Explanation:

Negishi Coupling:

• It involves the cross-coupling of an organohalide with the organozinc compound in the presence of Ni or Pd compounds.
• The leaving groups 'X' are generally halides or triflate. Palladium catalysts usually have high chemical yields and functional group tolerance.

​

Concept:

The reaction follows McMurry Mechanism  

McMurry Reaction:

• It's the reaction in which reductive dimerization of carbonyl compounds gives alkenes in the presence of TiCl3 and a reducing agent like Zn/Cu or LiAlH4.
• The reaction is inactive in finely divided Ti but works in a faster rate in TiCl3 + AlCl3 as it gives an electron rich Ti (0) particle.
• The reaction proceeds in two steps, ​radical coupling followed by deoxygenation on the surface of Ti(0). 

                Example: 
​

Explanation: 

The mechanism of the reaction involves radical bond cleavage followed by hydrolysis gives cyclic ketone.

Conclusion: 

Therefore option (2) is the correct one.

Explanation: -

The reaction will involve the following steps: -

Step 1: Oxidative-addition i.e. addition of organic compound on metal complex via sigma complex state with an increase in oxidation state on the metal ion.

Step 2: Transmetalation rearrangement reaction, this reaction involves the transfer of ligands from one metal to another metal complex.

Step 3: Reduction-elimination reaction, in this reaction metal, will undergo reduction by two oxidation states and two of the ligand will leave and form a single molecular species.

Conclusion: -

The reaction will produce the product preserved stereochemistry as follows: -

Hence, The correct option is - 2.

Concept:

Wittig reaction:

• In the Wittig reaction, an aldehyde or a ketone is reacted with a triphenyl phosphonium ylide to yield an alkene along with triphenylphosphine oxide.
• An example is shown below:

​

Claisen rearrangement:

• In a claisen rearrangement reaction, the allyl vinyl ether is converted into a gamma, delta-unsaturated carbonyl compound on heating or in presence of a Lewis acid.
• An example is shown below:

Cope rearrangement:

• The Cope rearrangement is a chemical reaction in organic chemistry that involves the [3,3]-sigmatropic rearrangement of 1,5-dienes on heating.
• An example is shown below:

Trans Esterification reaction:

• The transesterification reaction is the process of exchanging the organic functional group R¹ of an ester with the organic group R² of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst.

Explanation:

• The reaction pathway is shown below:

• From the above reaction, we can see that the phosphonium ylide reacts with the aldehyde to form the alkene.
• In the next step, the generated alkene undergoes a [3,3] Claisen rearrangement reaction followed by a [3,3] Cope rearrangement reaction.
• In the next step, the intermediate product undergoes an [1,5] H shift followed by a transesterification reaction to give the final product.

Conclusion:

Hence, the major product formed in the following reaction sequence is 

Concept:-

ZnCl₂ (Zinc Chloride): ZnCl₂ is a Lewis acid and is often used as a catalyst in organic synthesis reactions, including Fischer indole synthesis, Friedel-Crafts acylation reactions, and the activation of alkyl halides in nucleophilic substitutions. It is also used to promote the formation of acyl chlorides from carboxylic acids by dehydration.

Explanation:-

Conclusion:-

So, the correct option is 1