Question 1

Which of the following statements best describes the principle behind infrared (IR) spectroscopy?

Accepted Answer

IR spectroscopy measures the absorption of electromagnetic radiation by a sample as a function of wavelength.

Question 2

A photon of light has energy given by which equation?

Accepted Answer

$$E = h
u$$

Question 3

Which region of the electromagnetic spectrum is most commonly used to study molecular vibrations?

Accepted Answer

Infrared (IR)

Question 4

What is the relationship between bond strength and IR stretching frequency?

Accepted Answer

Stronger bonds absorb at higher frequencies.

Question 5

Which of the following bonds would you expect to have the highest IR stretching frequency?

Accepted Answer

C≡C triple bond

Question 6

A molecule with no dipole moment will:

Accepted Answer

Not absorb IR radiation (IR-inactive).

Question 7

Which functional group is characterized by a broad IR absorption centered around 3300 cm$$^{-1}$$?

Accepted Answer

Alcohol

Question 8

The IR spectrum of a carboxylic acid typically shows:

Accepted Answer

A broad O–H stretch from 2500–3500 cm$$^{-1}$$ and a C=O stretch at 1710 cm$$^{-1}.$$

Question 9

Which of the following statements about the fingerprint region in IR spectroscopy is correct?

Accepted Answer

The fingerprint region is below 1500 cm$$^{-1}$$ and contains complex bending and stretching vibrations unique to each molecule.

Question 10

Which IR absorption would you expect for a primary amine (RNH$$_2$$)?

Accepted Answer

Two sharp spikes at 3300 cm$$^{-1}.$$

Question 11

Which of the following would NOT be detected in a mass spectrometer?

Accepted Answer

Neutral molecules

Question 12

A mass spectrum of a compound containing bromine will show:

Accepted Answer

Two molecular ion peaks (M+ and M+2) of nearly equal intensity.

Question 13

Which fragmentation pattern is most common for alkenes in mass spectrometry?

Accepted Answer

Formation of the allylic cation.

Question 14

Which IR absorption is characteristic of a nitrile group?

Accepted Answer

Just above 2200 cm$$^{-1} ($$sharp)

Question 15

Which of the following statements about mass spectrometry is TRUE?

Accepted Answer

Mass spectrometry can determine the molecular weight and formula of a compound.

Question 16

Which of the following would result in a lower IR stretching frequency for a C=O bond?

Accepted Answer

Conjugation with a double bond.

Question 17

Which IR absorption is most likely to be observed for an ester functional group?

Accepted Answer

About 1735 cm$$^{-1}$$

Question 18

A molecule containing only C, H, O, and X (halogen) atoms will have:

Accepted Answer

Even molecular weight and most major fragments are odd-numbered.

Question 19

Which of the following is a plausible explanation for why symmetrical alkynes do not show a C≡C stretching absorption in IR spectra?

Accepted Answer

Symmetrical alkynes have no dipole moment, so the C≡C stretch is IR-inactive.

Infrared Spectroscopy and Mass Spectrometry: Principles and Applications

Study Guide - Practice Questions