Question 1

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

Accepted Answer

Conjugated alkenes allow for delocalization of $$\pi$$ electrons across multiple atoms, which lowers the overall energy of the molecule.

Question 2

Which of the following reagents would you use to synthesize an ether via the Williamson ether synthesis?

Accepted Answer

An alkoxide ion and a primary alkyl halide

Question 3

A student reacts 1-butanol with concentrated $$\ce{H_2SO_4}$$ under heat. What is the major organic product?

Accepted Answer

Di-n-butyl ether

Question 4

Which of the following best describes the difference between the kinetic and thermodynamic products in the alkylation of enolates?

Accepted Answer

The kinetic product forms faster and is less stable, while the thermodynamic product forms slower but is more stable.

Question 5

Which of the following is the correct IUPAC name for the compound commonly known as tetrahydrofuran?

Accepted Answer

Oxolane

Question 6

In the Diels-Alder reaction, why is the endo product usually favored over the exo product?

Accepted Answer

Secondary orbital interactions between the diene and the dienophile stabilize the endo transition state.

Question 7

Which of the following statements about the UV-Vis spectra of conjugated alkenes is correct?

Accepted Answer

Conjugated alkenes absorb at longer wavelengths than non-conjugated alkenes due to a smaller HOMO-LUMO gap.

Question 8

Which of the following best describes the mechanism for the acid-catalyzed opening of an epoxide?

Accepted Answer

The nucleophile attacks the more substituted carbon after protonation of the epoxide oxygen.

Question 9

Which of the following is a correct statement about the molecular orbital (MO) diagram for 1,3-butadiene?

Accepted Answer

The HOMO is $$\$$psi_2$$ and the LUMO is $$\$$psi_3.$$

Question 10

A chemist wants to synthesize an ether from 2-bromopropane and sodium methoxide. What is the expected major product?

Accepted Answer

No reaction, because 2-bromopropane is secondary and prone to elimination.

Question 11

Which of the following best explains why an electron-rich diene and an electron-poor dienophile are favored in the Diels-Alder reaction?

Accepted Answer

The electron-rich diene raises the energy of the HOMO, and the electron-poor dienophile lowers the energy of the LUMO, making the reaction more favorable.

Question 12

Which of the following is a property of ethers that makes them useful as solvents in organic reactions?

Accepted Answer

They are generally unreactive toward strong bases and nucleophiles.

Question 13

A compound with the formula $$\ce{C_4H_8O}$$ shows a strong IR absorption at $$1100\ \mathrm{cm}^{-1}$$ and no absorption near $$1700\ \mathrm{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Ether

Question 14

Which of the following best describes the regiochemistry of the Diels-Alder reaction between 1,3-butadiene and acrylonitrile ($$\ce{CH_2$=CHCN}$$)?

Accepted Answer

The cyano group ends up ortho or para to the newly formed ring double bond due to resonance stabilization.

Question 15

Which of the following statements about the opening of epoxides under basic conditions is correct?

Accepted Answer

The nucleophile attacks the less substituted carbon of the epoxide.

Question 16

Which of the following is the correct common name for 1,4-dioxane?

Accepted Answer

Dioxane

Question 17

A student analyzes the $$^1H $$NMR spectrum of a reaction mixture and observes the disappearance of a singlet at $$\delta = 2.1$$ ppm and the appearance of a new singlet at $$\delta = 3.4$$ ppm. What does this most likely indicate?

Accepted Answer

Conversion of a methyl ketone to an ether

Question 18

Which of the following best explains why the carbocation intermediate in the addition of HBr to 1,3-butadiene forms preferentially at the 2-position?

Accepted Answer

The carbocation at the 2-position is resonance stabilized by delocalization over two carbons.

Question 19

Which of the following is the correct order of steps for the acid-catalyzed formation of an ether from two alcohols?

Accepted Answer

Protonation of alcohol, loss of water to form carbocation, nucleophilic attack by second alcohol, deprotonation

Ethers, Epoxides, Conjugated Alkenes, and Cycloaddition Reactions: Mechanisms, Properties, and Spectroscopy

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