Question 1

Which region of the electromagnetic spectrum is primarily used in proton nuclear magnetic resonance ($$ ^1\mathrm{H} $$ NMR) spectroscopy?

Accepted Answer

Radio frequency region

Question 2

A compound shows a strong, broad absorption around $$3300\ \mathrm{cm}^{-1}$$ and a sharp absorption near $$1700\ \mathrm{cm}^{-1} in $$its IR spectrum. Which functional group is most likely present?

Accepted Answer

Carboxylic acid

Question 3

Which equation correctly relates the energy of electromagnetic radiation to its frequency?

Accepted Answer

$$E = hv$$

Question 4

A molecule has the formula $$\mathrm{C}_6\mathrm{H}_5\mathrm{NO}_2. $$What is its index of hydrogen deficiency (IHD)?

Accepted Answer

5

Question 5

In $$^1H $$NMR, what does the splitting pattern (multiplicity) of a signal reveal about a proton environment?

Accepted Answer

The number of vicinal (neighboring) protons to the proton(s) giving the signal

Question 6

A compound's IR spectrum shows a sharp absorption at $$2250\ \mathrm{cm}^{-1}. $$Which functional group is most likely responsible for this absorption?

Accepted Answer

Nitrile

Question 7

Which of the following statements about $$^{13}C $$NMR is TRUE?

Accepted Answer

Each nonequivalent carbon produces a distinct peak.

Question 8

A $$^1H $$NMR spectrum of a compound shows a quartet at $$\delta = 4.1$$ ppm integrating to 2H and a triplet at $$\delta = 1.2$$ ppm integrating to 3H. Which structure is most consistent with this data?

Accepted Answer

CH$$_3CH$_2OH ($$ethanol)

Question 9

Which of the following best explains why tetramethylsilane (TMS) is used as a reference in $$^1H $$NMR spectroscopy?

Accepted Answer

It has a single sharp peak at 0 ppm and is chemically inert.

Question 10

A compound absorbs UV light at a longer wavelength (higher $$\lambda_{max}) $$than benzene. Which structural feature is most likely responsible?

Accepted Answer

A more conjugated $$\pi$$ system

Question 11

Which of the following $$^1H $$NMR signals would you expect for the hydrogens in cyclohexane at room temperature?

Accepted Answer

One singlet

Question 12

A $$^1H $$NMR spectrum shows a singlet at $$\delta = 9.8$$ ppm. Which functional group is most likely present?

Accepted Answer

Aldehyde

Question 13

Which of the following IR absorptions is characteristic of an O-H stretch in alcohols?

Accepted Answer

$$3200-3600\ \mathrm{cm}^{-1}$$, broad

Question 14

A $$^1H $$NMR spectrum of a compound shows two signals: a triplet at $$\delta = 1.0$$ ppm (3H) and a quartet at $$\delta = 2.3$$ ppm (2H). Which compound is most consistent with this data?

Accepted Answer

Propionitrile

Question 15

Which of the following statements about spin-spin splitting in $$^1H $$NMR is correct?

Accepted Answer

A methylene group adjacent to a methyl group will appear as a triplet.

Question 16

Which of the following best describes the effect of electron-withdrawing groups on the chemical shift of nearby protons in $$^1H $$NMR?

Accepted Answer

They deshield the protons, causing a downfield shift.

Question 17

A compound has the molecular formula $$\mathrm{C}_4\mathrm{H}_8\mathrm{O}_2$$ and shows a strong IR absorption at $$1740\ \mathrm{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Ester

Question 18

Which of the following is a correct statement about $$^{13}C $$NMR compared to $$^1H $$NMR?

Accepted Answer

$$^{13}C $$NMR does not show splitting due to neighboring carbons.

Question 19

A sample is analyzed by UV-Vis spectroscopy and shows a $$\lambda_{max} at$$ $$350 nm. $$What does this suggest about the molecule?

Accepted Answer

It contains a highly conjugated $$\pi$$ system.

Chapter 14: Spectroscopy – Principles and Applications in Organic Chemistry

Guida di studio - Domande di pratica

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