Question 1

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

Accepted Answer

Conjugated dienes have greater electron delocalization, resulting in resonance stabilization.

Question 2

Which of the following is the correct IUPAC name for the compound shown below?

$$\mathrm{CH_2$=CHCH=CH_2$}$$

Accepted Answer

1,3-butadiene

Question 3

What is the bond angle around each carbon in ethylene ($$\mathrm{C_2H_4}$$)?

Accepted Answer

$$120^\circ$$

Question 4

Which of the following statements about the molecular orbitals of 1,3-butadiene is correct?

Accepted Answer

There are two bonding and two antibonding $$\pi$$ molecular orbitals.

Question 5

Which of the following best describes the product distribution when HBr is added to 1,3-butadiene at $$-80^\circC$$?

Accepted Answer

The 1,2-addition product predominates due to kinetic control.

Question 6

Which of the following is a cumulated diene?

Accepted Answer

$$\mathrm{CH_2$=C=CH_2$}$$

Question 7

Which of the following statements about the Diels-Alder reaction is FALSE?

Accepted Answer

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

Question 8

Which of the following substituents on a dienophile will most strongly increase the rate of a Diels-Alder reaction?

Accepted Answer

$$-\mathrm{COOR}$$

Question 9

Which of the following best describes the difference in bond lengths in 1,3-butadiene?

Accepted Answer

The central C–C bond is shorter than a typical single bond due to partial double bond character.

Question 10

Which of the following is the major product when 1,3-butadiene reacts with Br$$_2 at $$high temperature?

Accepted Answer

The 1,4-dibromo product

Question 11

Which of the following best explains why the endo product is favored in the Diels-Alder reaction?

Accepted Answer

Secondary orbital interactions stabilize the endo transition state.

Question 12

Which of the following statements about the SN2 reactivity of allylic halides is correct?

Accepted Answer

Allylic halides react faster due to stabilization of the transition state by conjugation.

Question 13

Which of the following is true regarding the resonance stabilization of the allyl cation?

Accepted Answer

The positive charge is delocalized over two carbons.

Question 14

Which of the following best describes the effect of temperature on the addition of HBr to 1,3-butadiene?

Accepted Answer

Low temperature favors the kinetic product, high temperature favors the thermodynamic product.

Question 15

Which of the following is a requirement for a diene to participate in a Diels-Alder reaction?

Accepted Answer

The diene must be able to adopt an s-cis conformation.

Question 16

Which of the following best describes the regiochemistry of the Diels-Alder reaction between a diene with an electron-donating group and a dienophile with an electron-withdrawing group?

Accepted Answer

The electron-donating and electron-withdrawing groups end up in a 1,4- or 1,2-relationship.

Question 17

Which of the following is the best explanation for why the C2–C3 bond in 1,3-butadiene is shorter than a typical single bond?

Accepted Answer

There is partial double bond character due to delocalization of $$\pi$$ electrons.

Question 18

Which of the following is a real-world application of the Diels-Alder reaction?

Accepted Answer

Synthesis of six-membered aromatic rings in pharmaceuticals.

Question 19

Which of the following best describes the molecular orbital interaction in the Diels-Alder reaction?

Accepted Answer

The highest occupied molecular orbital (HOMO) of the diene interacts with the lowest unoccupied molecular orbital (LUMO) of the dienophile.

Conjugated Systems, Orbital Symmetry, and Dienes: Structure, Stability, and Reactivity

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