Question 1

Which of the following statements best explains why conjugated dienes are more stable than isolated dienes?

Accepted Answer

Conjugated dienes have delocalized electrons, which lowers their overall energy.

Question 2

The heat of hydrogenation for trans-1,3-pentadiene is measured to be $$-225\ \mathrm{kJ}$$, while the predicted value for two isolated double bonds is $$-242\ \mathrm{kJ}. $$What does this difference indicate?

Accepted Answer

Trans-1,3-pentadiene is more stable than two isolated double bonds by $$17\ \mathrm{kJ}.$$

Question 3

Which of the following best describes the requirement for the diene in a Diels–Alder reaction?

Accepted Answer

The diene must be in the s-cis conformation to react.

Question 4

Which of the following groups is an electron-withdrawing group (EWG) that would activate a dienophile in a Diels–Alder reaction?

Accepted Answer

$$-\mathrm{COOH}$$

Question 5

In the Diels–Alder reaction, what is the major product when 1,3-butadiene reacts with maleic acid? (Refer to the image with four possible cyclohexene products labeled I–IV.)

Accepted Answer

Product I

Question 6

Why does cyclopentadiene react much faster in Diels–Alder reactions compared to 1,3-butadiene?

Accepted Answer

Cyclopentadiene is locked in the s-cis conformation, which is required for the reaction.

Question 7

Which of the following best describes the 'endo rule' in the Diels–Alder reaction?

Accepted Answer

The endo product is favored due to secondary orbital overlap between the diene and electron-withdrawing groups on the dienophile.

Question 8

Which of the following dienes will NOT undergo a Diels–Alder reaction under normal conditions?

Accepted Answer

Benzene

Question 9

A student reacts 2,3-dimethyl-1,3-butadiene with dimethyl maleate in a Diels–Alder reaction. Which of the following is the expected product?

Accepted Answer

A cyclohexene ring with two methyl and two ester groups in a cis relationship.

Question 10

Which of the following statements about the transition state of the Diels–Alder reaction is correct?

Accepted Answer

The transition state involves the formation of two new sigma bonds and secondary orbital overlap.

Question 11

Which of the following best explains why the s-trans conformation of 1,3-butadiene is more stable than the s-cis conformation?

Accepted Answer

The s-trans conformation has less steric strain between substituents.

Question 12

Which of the following is a correct retrosynthetic analysis for a cyclohexene ring formed via a Diels–Alder reaction?

Accepted Answer

Break the cyclohexene ring into a 1,3-diene and a dienophile.

Question 13

Which of the following is the major product when benzene reacts with 1-methoxy-1,3-butadiene in a Diels–Alder reaction? (Refer to the image with four possible bicyclic products labeled I–IV.)

Accepted Answer

Product II

Question 14

Which of the following statements about the reactivity of dienes in Diels–Alder reactions is correct?

Accepted Answer

Dienes locked in the s-cis conformation react faster than those that are not.

Question 15

Which of the following best describes the relationship between electron-donating groups (EDG) and the diene in a Diels–Alder reaction?

Accepted Answer

EDGs increase the nucleophilicity of the diene, making it more reactive.

Question 16

A Diels–Alder reaction is performed with an unsymmetrical diene and an unsymmetrical dienophile. Which of the following is most likely observed in the product mixture?

Accepted Answer

A mixture of 1,2- and 1,4-addition products.

Question 17

Which of the following best explains why allylic halides are more reactive in $$\mathrm{S_N2}$$ reactions than non-allylic halides?

Accepted Answer

The transition state is stabilized by conjugation with the pi system.

Conjugated Systems and Diels–Alder Reactions: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard