Question 1

Which of the following statements best explains why conjugation in a molecule causes a bathochromic (red) shift in its UV-Vis absorption spectrum?

Accepted Answer

Conjugation decreases the energy gap between the HOMO and LUMO, allowing absorption of lower energy (longer wavelength) photons.

Question 2

A chemist performs a Friedel-Crafts alkylation of benzene using tert-butyl chloride and AlCl$$_3. $$Which of the following is the major product?

Accepted Answer

tert-Butylbenzene

Question 3

Given the following $$^1H $$NMR data for a compound: a singlet at $$\delta = 2.1$$ ppm (3H), a quartet at $$\delta = 2.5$$ ppm (2H), and a triplet at $$\delta = 1.0$$ ppm (3H), which compound is most likely represented?

Accepted Answer

Butanone

Question 4

Which of the following best describes the effect of shielding in NMR spectroscopy?

Accepted Answer

Shielding causes nuclei to absorb at lower chemical shift values (upfield).

Question 5

In a Diels-Alder reaction between 1,3-butadiene and ethene, what is the product?

Accepted Answer

Cyclohexene

Question 6

Which of the following statements about reversible and irreversible nucleophilic attacks in conjugate addition is correct?

Accepted Answer

Irreversible nucleophilic attacks favor 1,2-direct addition.

Question 7

A student is given the IR spectrum of an unknown compound showing a strong absorption at $$\nu = 1715 cm$^{-1}. $$Which functional group is most likely present?

Accepted Answer

Ketone

Question 8

Which of the following compounds would show the greatest chemical shift (deshielding) for its aromatic protons in $$^1H $$NMR?

Accepted Answer

Nitrobenzene

Question 9

When using NaBH$$_4 in $$methanol to reduce a compound, which functional group will be selectively reduced?

Accepted Answer

Ketone

Question 10

Which of the following best describes the mechanism of the Friedel-Crafts acylation reaction?

Accepted Answer

Electrophilic aromatic substitution involving an acylium ion intermediate

Question 11

A compound has the empirical formula C$$_4H$_8O. $$Its $$^1H $$NMR shows a triplet at $$\delta = 1.0$$ ppm (3H), a quartet at $$\delta = 2.3$$ ppm (2H), and a singlet at $$\delta = 2.1$$ ppm (3H). Which structure fits this data?

Accepted Answer

2-Butanone

Question 12

Which of the following is true regarding the locations of potential nucleophilic attack in $$\alpha,\beta-$$unsaturated carbonyl compounds?

Accepted Answer

Nucleophilic attack can occur at both the carbonyl carbon (1,2-addition) and the $$\beta-$$carbon (1,4-addition).

Question 13

Which of the following best explains why the $$^1H $$NMR chemical shift of a proton adjacent to an electronegative atom (such as oxygen) is higher than that of a proton adjacent to a carbon atom?

Accepted Answer

Electronegative atoms deshield nearby protons, causing a higher chemical shift.

Question 14

A molecule with extended conjugation absorbs light at a longer wavelength than a similar molecule without conjugation. Which molecular orbital theory concept explains this observation?

Accepted Answer

Conjugation decreases the HOMO-LUMO gap.

Question 15

Which of the following is NOT a requirement for a successful Friedel-Crafts alkylation?

Accepted Answer

Electron-withdrawing substituents on the aromatic ring

Question 16

A chemist wants to predict the product of a Diels-Alder reaction between cyclopentadiene and maleic anhydride. What is the major product?

Accepted Answer

A bicyclic compound with two anhydride groups

Question 17

Which of the following statements about $$^1H $$NMR is correct?

Accepted Answer

Chemically distinct protons have different chemical shifts.

Question 18

Which of the following best describes the effect of deshielding in NMR spectroscopy?

Accepted Answer

Deshielding causes nuclei to absorb at higher chemical shift values (downfield).

Question 19

A student is given the $$^1H $$NMR spectrum of ethylbenzene. Which set of signals would you expect to see?

Accepted Answer

A singlet for the methyl group, a quartet for the methylene group, and a multiplet for the aromatic protons.

Organic Chemistry Mechanisms, Spectroscopy, and Reaction Pathways: Study Notes

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