GATE Chemistry Practice Quiz

Question 1

Under thermal conditions, electrocyclic ring closure of (2E,4E)-hexadiene gives which stereochemical outcome for the two terminal methyl groups in cyclobutene product?

Accepted Answer

trans-3,4-dimethylcyclobutene

Question 2

A thermal Diels-Alder reaction between cyclopentadiene and maleic anhydride gives predominantly which stereochemical product under kinetic control?

Accepted Answer

Endo adduct due to secondary orbital interactions

Question 3

For thermal electrocyclic ring opening of trans-3,4-dimethylcyclobutene, the stereochemistry of the resulting diene is predicted to be

Accepted Answer

(2E,4E)-hexadiene

Question 4

A chiral, nonracemic allene undergoes a thermal 6π electrocyclic ring closure embedded in a hexatriene framework. Which general stereochemical principle best explains why the product can be formed with high torquoselectivity?

Accepted Answer

Substituents rotate in the direction that minimizes unfavorable orbital and steric interactions in the allowed mode

Question 5

Photochemical electrocyclic ring closure of a 4π system such as butadiene occurs by which mode of terminal rotation?

Accepted Answer

Disrotatory

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