Question 1

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

Accepted Answer

Because conjugated dienes have more resonance structures due to delocalization of $$\pi$$ electrons.

Question 2

What is the hybridization of all the carbons in 1,3-butadiene?

Accepted Answer

All carbons are $$sp^2$$ hybridized.

Question 3

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

Accepted Answer

The reaction proceeds through a carbocation intermediate.

Question 4

Which product is favored at low temperature in the electrophilic addition of HBr to 1,3-butadiene?

Accepted Answer

The 1,2-adduct (kinetic product)

Question 5

Given the following reaction: $$\mathrm{CH_2$=CH-CH=CH_2$ + HBr} at$$ $$0^\circ C$$, which is the major product?

Accepted Answer

$$\mathrm{CH_2Br-CH=CH-CH_3$} (1$$,2-adduct)

Question 6

Which of the following dienophiles would react fastest in a Diels-Alder reaction with 1,3-butadiene?

Accepted Answer

Maleic anhydride

Question 7

Why is the central C–C bond in 1,3-butadiene shorter than a typical single bond?

Accepted Answer

Because of partial double bond character due to $$\pi$$ electron delocalization.

Question 8

Which of the following best describes the molecular orbitals formed in 1,3-butadiene?

Accepted Answer

Two bonding and two antibonding $$\pi$$ molecular orbitals.

Question 9

Which of the following conditions will favor the formation of the thermodynamic product in the addition of HBr to a conjugated diene?

Accepted Answer

High temperature and long reaction time

Question 10

In the Diels-Alder reaction, which conformation must the diene adopt to react?

Accepted Answer

s-cis

Question 11

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

Accepted Answer

The stereochemistry of the dienophile is retained in the product.

Question 12

Which of the following best explains the increased stability of the allylic carbocation?

Accepted Answer

It is stabilized by resonance delocalization of the positive charge.

Question 13

Which of the following is a requirement for a dienophile to be highly reactive in a Diels-Alder reaction?

Accepted Answer

It must have electron-withdrawing groups such as $$-CN or$$ $$-C=O.$$

Question 14

Which of the following best describes the difference between kinetic and thermodynamic control in the addition of HX to conjugated dienes?

Accepted Answer

Kinetic control gives the fastest forming product, thermodynamic control gives the most stable product.

Question 15

Which of the following is NOT a characteristic of pericyclic reactions such as the Diels-Alder reaction?

Accepted Answer

They proceed through ionic intermediates.

Question 16

A Diels-Alder reaction between cyclopentadiene and maleic anhydride gives a bicyclic product. Which position is favored for the electron-withdrawing groups of the dienophile?

Accepted Answer

Endo position

Question 17

Which of the following best describes the product of the Diels-Alder reaction between 1,3-butadiene and ethylene?

Accepted Answer

A six-membered ring with no double bonds (cyclohexane)

Question 18

Which of the following statements about resonance in conjugated dienes is correct?

Accepted Answer

Resonance decreases the energy and increases the stability of the molecule.

Question 19

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

Accepted Answer

Synthesis of six-membered rings in pharmaceuticals

Dienos Conjugados y la Reacción de Diels-Alder: Estructura, Estabilidad y Reactividad

Study Guide - Practice Questions

Study Guide - Flashcards