Q: Which equation correctly relates the energy of electromagnetic radiation to its frequency and wavelength?

$$E = h \nu = \dfrac{hc}{\lambda}$$

Q: Which of the following is the correct formula for calculating the relative abundance of the M$$+1$$ peak in a mass spectrum due to $$^{13}C$$?

$$(\text{number of carbons}) \times 0.0111$$

Question 1

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

Accepted Answer

$$E = h 
u = \dfrac{hc}{\lambda}$$

Question 2

A molecule shows a strong IR absorption at $$1700\ 	ext{cm}^{-1}$$ and two weak peaks at $$2720$$ and $$2820\ 	ext{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Aldehyde

Question 3

Which region of the IR spectrum is known as the 'fingerprint region'?

Accepted Answer

$$400-1500\ 	ext{cm}^{-1}$$

Question 4

A mass spectrum shows a molecular ion peak (M$$^+) at$$ $$m/z = 86$$ and a significant M$$+2$$ peak of equal intensity. Which element is most likely present in the molecule?

Accepted Answer

Bromine

Question 5

Which of the following statements about NMR spectroscopy is correct?

Accepted Answer

NMR provides information about the number, connectivity, and environment of hydrogens and carbons in a molecule.

Question 6

A compound has a molecular formula of $$C_4H_{10}O$$ and its $$^1H $$NMR spectrum shows four signals in the ratio 2:1:1:6. Which structure is most consistent with this data?

Accepted Answer

2-methyl-1-propanol

Question 7

Which of the following best explains why 3-hexyne does not show an IR absorption in the range $$2000-2200\ 	ext{cm}^{-1}$$, while 1-hexyne does?

Accepted Answer

3-hexyne is a symmetrical compound with no change in bond dipole during vibration.

Question 8

Which of the following is a limitation of IR spectroscopy?

Accepted Answer

IR alone cannot determine the complete structure of a molecule.

Question 9

A mass spectrum of a hydrocarbon shows an M$$^+$$ peak at $$m/z = 72$$ and an M$$+1$$ peak at $$m/z = 73$$ with a relative intensity of 3.3%. How many carbons are in the molecule?

Accepted Answer

4

Question 10

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

Accepted Answer

A proton with $$n$$ neighboring protons will appear as an $$(n+1)-$$multiplet.

Question 11

Which of the following is the correct formula for calculating the relative abundance of the M$$+1$$ peak in a mass spectrum due to $$^{13}C$$?

Accepted Answer

$$(	ext{number of carbons}) 	imes 0.0111$$

Question 12

Which of the following nuclei is NOT commonly observed in NMR spectroscopy?

Accepted Answer

$$^{12}	ext{C}$$

Question 13

Which of the following best describes the effect of electron shielding on the chemical shift in $$^1H $$NMR?

Accepted Answer

Shielded protons absorb at higher field (upfield, lower ppm) than deshielded protons.

Question 14

A compound gives a strong IR absorption at $$3300\ 	ext{cm}^{-1}$$ and a medium absorption at $$2150\ 	ext{cm}^{-1}. $$Which functional group is most likely present?

Accepted Answer

Terminal alkyne

Question 15

Which of the following statements about the Williamson ether synthesis is correct?

Accepted Answer

The SN2 reaction is most successful when the alkyl halide is primary and the alkoxide is bulky.

Question 16

Which of the following is a correct interpretation of the following $$^1H $$NMR data: a singlet at $$\delta = 2.1 (3H$$), a quartet at $$\delta = 4.1 (2H$$), and a triplet at $$\delta = 1.2 (3H$$)?

Accepted Answer

An ethyl group attached to an oxygen atom (ethyl ether or ethyl ester)

Question 17

Which of the following is true about the base peak in a mass spectrum?

Accepted Answer

It is the ion of greatest relative abundance in the spectrum.

Question 18

Which of the following best describes the effect of an external magnetic field on nuclear spin states in NMR?

Accepted Answer

It causes the spin states to have different energies, allowing resonance to occur.

Question 19

A compound with the formula $$C_4H_8O_2$$ shows a broad IR absorption from $$2200-3600\ 	ext{cm}^{-1}$$, a strong absorption at $$1720\ 	ext{cm}^{-1}$$, and another at $$1200\ 	ext{cm}^{-1}. $$Which functional groups are most likely present?

Accepted Answer

Carboxylic acid and ester

Spectroscopy and Structure Determination in Organic Chemistry: IR, Mass Spectrometry, and NMR

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