Question 1

Which statement best describes the molecular ion (M*) in mass spectrometry?

Accepted Answer

It is a radical cation formed when a molecule loses an electron.

Question 2

In the mass spectrum of methane ($$\mathrm{CH_4$}$$), the base peak corresponds to:

Accepted Answer

The molecular ion with $$m/z = 16$$

Question 3

A compound containing bromine ($$\mathrm{Br}) $$will show two molecular ion peaks in its mass spectrum. What is the approximate ratio of their intensities?

Accepted Answer

$$1:1$$

Question 4

Which equation correctly relates the energy of a photon to its frequency in infrared spectroscopy?

Accepted Answer

$$E = h 	imes v$$

Question 5

In IR spectroscopy, which region is most useful for identifying functional groups?

Accepted Answer

Functional group region ($$1500$$–$$4000 cm$^{-1})$$

Question 6

A mass spectrum of an unknown organic compound shows a molecular ion peak at $$m/z = 78$$ and a significant $$M+2$$ peak at $$m/z = 80$$ with a $$3:1$$ intensity ratio. Which element is most likely present?

Accepted Answer

Chlorine ($$\mathrm{Cl})$$

Question 7

Which type of fragmentation is commonly observed in carbonyl compounds during mass spectrometry?

Accepted Answer

Alpha-cleavage, breaking the bond adjacent to the carbonyl carbon

Question 8

Why does the $$M+1$$ peak appear in the mass spectrum of methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

Due to the natural abundance of carbon-13 isotope

Question 9

Which of the following bonds would absorb at the highest wavenumber in an IR spectrum?

Accepted Answer

C–H (sp)

Question 10

A student analyzes an unknown compound by IR spectroscopy and observes a strong absorption near $$1700 cm$^{-1}. $$Which functional group is most likely present?

Accepted Answer

Carbonyl ($$\mathrm{C=O})$$

Question 11

Which statement about the base peak in a mass spectrum is correct?

Accepted Answer

It is the tallest peak and represents the most abundant ion.

Question 12

In mass spectrometry, what does the $$m/z$$ value represent?

Accepted Answer

The ratio of mass to charge of the ion

Question 13

Which of the following is a common fragmentation pattern for alcohols in mass spectrometry?

Accepted Answer

Alpha-cleavage to form a resonance-stabilized carbocation

Question 14

If a compound shows a strong IR absorption at $$3300 cm$^{-1}$$, which functional group is most likely responsible?

Accepted Answer

Alcohol ($$\mathrm{-OH})$$

Question 15

Which of the following statements about high-resolution mass spectrometry (HRMS) is correct?

Accepted Answer

HRMS measures $$m/z$$ values to several decimal places, allowing distinction between compounds with similar molecular weights.

Question 16

A mass spectrum of an unknown shows two peaks at $$m/z = 122$$ and $$m/z = 124 of $$equal intensity. Which element is most likely present?

Accepted Answer

Bromine ($$\mathrm{Br})$$

Question 17

Which equation correctly relates the speed of light ($$c$$), wavelength ($$\lambda$$), and frequency ($$v) in IR $$spectroscopy?

Accepted Answer

$$c = \lambda 	imes v$$

Question 18

In IR spectroscopy, what effect does conjugation with a C=C bond or benzene ring have on the $$\mathrm{C=O}$$ absorption band?

Accepted Answer

It lowers the wavenumber of absorption.

Question 19

Which of the following is NOT a main method of characterization in organic chemistry?

Accepted Answer

Ultraviolet-visible spectroscopy (UV-Vis)

Question 20

A student observes a strong IR absorption at $$2250 cm$^{-1} in a $$compound. Which functional group is most likely present?

Accepted Answer

Alkyne ($$\mathrm{C\equiv C})$$

Spectroscopy A & B: Mass Spectrometry and Infrared Spectroscopy

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