Question 1

Which region of the electromagnetic spectrum is most commonly used for structural confirmation in pharmaceutical IR spectroscopy?

Accepted Answer

Mid Infrared (2,500–50,000 nm)

Question 2

Why do molecules like $$\mathrm{N_2$}$$ and $$\mathrm{O_2$}$$ not show IR absorption bands?

Accepted Answer

They lack a permanent dipole moment during vibration.

Question 3

According to Hooke’s Law, which factor most directly increases the vibrational frequency of a chemical bond?

Accepted Answer

Increasing the force constant ($$k)$$

Question 4

A pharmaceutical chemist observes a strong, broad absorption near 3300 cm$$^{-1} in an IR $$spectrum. Which functional group is most likely present?

Accepted Answer

Alcohol

Question 5

Which of the following best explains why the C=O stretch appears at different wavenumbers for ketones, aldehydes, and carboxylic acids?

Accepted Answer

The chemical environment and conjugation affect the force constant ($$k) of $$the C=O bond.

Question 6

A sample is analyzed by IR and shows a sharp absorption at 2100–2200 cm$$^{-1}$$ and another at around 3300 cm$$^{-1}. $$Which compound is most likely present?

Accepted Answer

Alkyne

Question 7

Which of the following sample preparation methods is most suitable for analyzing a solid pharmaceutical tablet by IR spectroscopy?

Accepted Answer

KBr disc method

Question 8

What is the main advantage of Fourier Transform (FT) IR spectrometers over dispersive IR spectrometers?

Accepted Answer

FT-IR spectrometers are much faster and can collect all wavelengths simultaneously.

Question 9

A pharmaceutical company needs to confirm the identity of a raw material using IR spectroscopy. Which feature of IR spectra is most useful for this purpose?

Accepted Answer

The fingerprint region (below 1500 cm$$^{-1})$$

Question 10

Which of the following statements about IR absorption intensity is correct?

Accepted Answer

It is proportional to the dipole moment change during vibration.

Question 11

A chemist is analyzing a cream formulation and wants to check for the presence of different polymorphs of a drug. Why is IR spectroscopy suitable for this application?

Accepted Answer

Polymorphs have different crystal structures, leading to unique IR spectra.

Question 12

Which of the following is a limitation of IR spectroscopy in pharmaceutical analysis?

Accepted Answer

It is rarely used as a quantitative technique due to the complexity of spectra.

Question 13

Given the Hooke’s Law equation for vibrational frequency: $$n = \frac{1}{2\pi} \sqrt{\frac{k}{m}}$$, what will happen to the vibrational frequency if the reduced mass ($$m) $$increases while $$k$$ remains constant?

Accepted Answer

The frequency will decrease.

Question 14

Which functional group is characterized by a strong absorption near 1700 cm$$^{-1} in an IR $$spectrum?

Accepted Answer

Ketone

Question 15

A student observes a broad absorption between 2400–3300 cm$$^{-1}$$ and a sharp peak at 1757 cm$$^{-1} in $$the IR spectrum of aspirin. Which functional groups do these correspond to?

Accepted Answer

Carboxylic acid O-H and ester C=O

Question 16

Which of the following best describes the main use of the Attenuated Total Reflectance (ATR) technique in IR spectroscopy?

Accepted Answer

It allows direct analysis of solids, liquids, and semi-solids without extensive sample preparation.

Question 17

Which of the following bonds would you expect to have the highest vibrational frequency in an IR spectrum, based on Hooke’s Law?

Accepted Answer

C≡C triple bond

Question 18

Why is the IR spectrum of a molecule considered a 'fingerprint' for that molecule?

Accepted Answer

Because the pattern of absorptions is unique to each molecule.

Question 19

Which of the following is NOT a typical use of IR spectroscopy in pharmaceutical analysis?

Accepted Answer

Quantitative analysis of trace impurities

Question 20

A pharmaceutical sample shows a strong absorption at 1690 cm$$^{-1}$$ and a broad band at 2400–3300 cm$$^{-1}. $$Which functional groups are most likely present?

Accepted Answer

Carboxylic acid (C=O and O–H)

Infrared Spectroscopy in Analytical Chemistry: Principles, Interpretation, and Applications

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