Pericyclic Level - 2 - Free MCQ Practice Test with solutions, Chemistry

[4+2] cycloaddition, COOMe remains as it is and stereochemistry of 2 Hydrogen remains cis.

In the given reaction, a benzene ring (C6H6) reacts with ethyl vinyl ketone (CO2Et) under heat (Δ). This is a typical reaction known as the Diels-Alder reaction.

The Diels-Alder reaction involves the reaction of a diene (in this case, the benzene ring acting as the diene) with a dienophile (ethyl vinyl ketone). The product formed in such a reaction is a cyclohexene derivative with the ethyl ester group.

Given the options:

• Option (a) shows a structure resembling the correct product formed by this reaction.

Therefore, the correct product for this reaction is option (a).

The reaction proceeds by a Diels-Alder cycloaddition between a conjugated diene and an electron-poor dienophile, giving a bicyclic adduct.

The endo product is favoured because of secondary orbital interactions between the dienophile's carbonyl π* and the diene π system; these interactions stabilise the transition state leading to the endo stereochemistry (the CO2R group oriented toward the newly formed bridging bond).

Coordination of the Lewis acid TiCl2(OPri)2 to the ester carbonyl lowers the dienophile LUMO, accelerating the reaction and further increasing endo selectivity; at 20°C the kinetically controlled endo product is predominant.

Therefore the major product is the endo bicyclic Diels-Alder adduct, which matches option A.

The major product of the reaction is option B. Here’s why:

• The reaction involves nucleophilic substitution, which is common in these types of organic reactions.
• In this scenario, the most suitable leaving group is replaced by the incoming nucleophile.
• Option B is the structure that results from this substitution, making it the correct major product.

Understanding the mechanism helps to identify the correct product:

• Electrophilic site: This is where the nucleophile attacks.
• Leaving group: A good leaving group makes the reaction proceed smoothly.
• Product formation: The final structure reflects the substitution that has taken place.

Six membered transition state of chair form will give option A.

The major product of the reaction is determined by the mechanism involved. Here's a breakdown:

• The reaction likely proceeds via a nucleophilic substitution mechanism.
• The substrate is most likely secondary or tertiary, favouring a SN1 mechanism.
• In a SN1 reaction, the carbocation intermediate forms, which is stabilised by the surrounding groups.
• The nucleophile then attacks this carbocation to form the product.