Question

Which of the following statements about the Diel-Alder reaction are true?

Which of the following statements about the Diels-Alder reaction are true? I. The Diels-Alder reaction is endothermic. II. The Diels-Alder reaction is exothermic. III. The Diels-Alder reaction is favored entropically. IV. The Diels-Alder reaction is disfavored entropically. V. The Diels-Alder reaction is favored at extremely high temperatures. VI. The Diels-Alder reaction is favored at room temperature to moderate temperature. (A) I, IlI, and VI (B) II, IV, V (C) II, IV, vI

Answer 1

A Diels-Alder involves the reaction of a diene with a dienophile to form a cyclohexene derivative. We can use bond dissociation energies ( D ) to calculate an approximate value of ΔH for this reaction. This is only a rough value, but it shows that the formation of four new C-C bonds makes the reaction quite .exothermic.

The yield of the Diels-Alder addition decreases with the temperature. With a temperature higher than 400K, we would favour the reverse reaction. This is due to the negative entropy that favours dissociation, and its importance increases with temperature.

so correct option is (C)