Question 1

Which of the following resonance contributors for the acetate ion ($\mathrm{CH_3COO^-}$) is the major contributor? Consider lone pairs, formal charges, and electron delocalization.

Accepted Answer

The structure with both oxygens sharing the negative charge equally, with delocalized electrons.

Question 2

Which of the following pairs contains the more acidic species?

A. $\mathrm{CH_3OH}$ vs. $\mathrm{CH_3O^-}$

B. $\mathrm{H_2O}$ vs. $\mathrm{H_3O^+}$

Accepted Answer

A: $\mathrm{CH_3OH}$; B: $\mathrm{H_3O^+}$

Question 3

In the addition of HBr to 1,3-butadiene at low temperature, which is the major product and why?

Accepted Answer

1,2-addition product due to kinetic control at low temperature.

Question 4

Which pair of starting materials can be used to synthesize the following Diels-Alder adduct: cyclohexene with a single double bond?

A. 1,3-butadiene and ethene
B. 1,3-butadiene and acetylene
C. 1,3-butadiene and 1,3-butadiene
D. Benzene and ethene

Accepted Answer

A. 1,3-butadiene and ethene

Question 5

In a Diels-Alder reaction between cyclopentadiene and maleic anhydride, what is the stereochemistry of the product?

Accepted Answer

Endo product is favored due to secondary orbital interactions.

Question 6

Using the Frost Circle diagram, which of the following is aromatic?

A. Cyclobutadiene
B. Benzene
C. Cyclooctatetraene
D. Cyclopentadiene anion

Accepted Answer

B. Benzene

Question 7

If the natural abundances of $^{35}\mathrm{Cl}$ and $^{37}\mathrm{Cl}$ are approximately 75% and 25%, respectively, what is the expected ratio of $(M)^+$, $(M+2)^+$, and $(M+4)^+$ peaks for a compound containing two chlorine atoms?

Accepted Answer

$9:6:1$

Question 8

A compound shows $(M)^+$ and $(M+1)^+$ peaks in a mass spectrum with a ratio of approximately $10:1$. How many carbon atoms are present in the molecule? (Assume $^{13}\mathrm{C}$ is 1.1% abundant.)

Accepted Answer

9

Question 9

Which of the following compounds is expected to absorb electromagnetic radiation between 200 and 300 nm?

A. Benzene
B. Cyclohexane
C. Methane
D. Ethanol

Accepted Answer

A. Benzene

Question 10

Using the Woodward-Fieser rules, which structure would have a higher $\lambda_{max}$ in UV-Vis spectroscopy?

A. 1,3-butadiene
B. 1,3,5-hexatriene

Accepted Answer

B. 1,3,5-hexatriene, because it has a longer conjugated system.

Question 11

How many distinct signals would you expect in the $^{13}\mathrm{C}$ NMR spectrum of 2,2-dimethylpropane (neopentane)?

Accepted Answer

1

Question 12

Which of the following compounds would give only one signal in its $^{13}\mathrm{C}$ NMR spectrum due to symmetry?

Accepted Answer

Tetramethylsilane ($\mathrm{Si(CH_3)_4}$)

Question 13

Which of the following best explains why the acetate ion ($\mathrm{CH_3COO^-}$) is stabilized by resonance?

Accepted Answer

The negative charge is delocalized over two oxygen atoms, lowering the energy of the ion.

Question 14

Which of the following is the best explanation for the higher acidity of phenol compared to cyclohexanol?

Accepted Answer

The phenoxide ion is stabilized by resonance with the aromatic ring.

Question 15

Which of the following is antiaromatic according to the Frost Circle diagram?

Accepted Answer

Cyclobutadiene

Question 16

A compound with the formula $\mathrm{C_6H_6}$ shows a single $^{13}\mathrm{C}$ NMR signal. Which compound is it?

Accepted Answer

Benzene

Question 17

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

Accepted Answer

Cyclohexene

Question 18

Which of the following is a kinetic product in the addition of HBr to 1,3-butadiene?

Accepted Answer

3-bromo-1-butene

Question 19

Which of the following compounds would you expect to have the highest $\lambda_{max}$ according to the Woodward-Fieser rules?

A. 1,3-butadiene
B. 1,3,5,7-octatetraene
C. 1,3,5-hexatriene
D. Ethene

Accepted Answer

B. 1,3,5,7-octatetraene

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