Question 1

How many unique $$^{1}\mathrm{H}$$ NMR signals would you expect for cyclopentane?

Accepted Answer

1

Question 2

Which of the following best describes the relationship between protons $$H_a$$ and $$H_b in 1$$,2-dichloropropane?

Accepted Answer

Diastereotopic

Question 3

Which of the following compounds is aromatic?

Accepted Answer

Pyridine

Question 4

In a Diels-Alder reaction, which diene would be the most reactive?

Accepted Answer

1,3-cyclopentadiene

Question 5

Which dienophile is the most reactive in a typical Diels-Alder reaction?

Accepted Answer

Acrylonitrile ($$CH_2=$$CHCN$$)

Question 6

Given the $$^{1}\mathrm{H}$$ NMR spectrum with a singlet at 2.1 ppm (3H) and a quartet at 4.1 ppm (2H), which structure is most consistent with these data?

Accepted Answer

Ethyl acetate

Question 7

Calculate the index of hydrogen deficiency (IHD) for a molecule with the formula $$C_4H_6O_2.$$

Accepted Answer

$$2$$

Question 8

Which of the following best explains why cyclobutadiene is anti-aromatic?

Accepted Answer

It has 4 $$\pi$$ electrons and is planar.

Question 9

In the addition of HBr to 1,3-butadiene, which product is favored at low temperature (kinetic control)?

Accepted Answer

1,2-addition product

Question 10

Which of the following IR absorptions would you expect for a carbonyl group?

Accepted Answer

$$1700\ \mathrm{cm}^{-1}$$

Question 11

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

Accepted Answer

The major product has electron-withdrawing groups oriented under the diene in the transition state.

Question 12

Which of the following is a correct statement about the $$^{13}\mathrm{C}$$ NMR spectrum of benzene?

Accepted Answer

It shows a single peak due to all carbons being equivalent.

Question 13

Which of the following dienes is least reactive in a Diels-Alder reaction?

Accepted Answer

trans-1,3-butadiene

Question 14

Which of the following is a correct statement about the thermodynamic product in the addition of HBr to 1,3-butadiene?

Accepted Answer

It is the 1,4-addition product and is more stable due to conjugation.

Question 15

Which of the following best explains why compound A (in the extra credit) is unstable and decomposes above $$-40\ ^\circ\mathrm{C}$$?

Accepted Answer

It is a highly strained intermediate that undergoes retro-Diels-Alder reaction.

Question 16

Which of the following best describes the relationship between $$H_a$$ and $$H_b in 1$$,2-dichloroethane?

Accepted Answer

Enantiotopic

Question 17

Which of the following is a correct statement about the IR spectrum of a carboxylic acid?

Accepted Answer

It shows a broad O-H stretch around $$2500-3300\ \mathrm{cm}^{-1}$$ and a C=O stretch near $$1700\ \mathrm{cm}^{-1}.$$

Question 18

Which of the following best explains why the exo product is usually the minor product in a Diels-Alder reaction?

Accepted Answer

The endo transition state is stabilized by secondary orbital interactions.

Question 19

Which of the following dienophiles would react fastest with cyclopentadiene in a Diels-Alder reaction?

Accepted Answer

Maleic anhydride

Organic Chemistry: NMR, Aromaticity, and Diels-Alder Reactions – Study Notes

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