Question 1

Which region of the infrared spectrum is most commonly used in IR spectroscopy for identifying functional groups in organic molecules?

Accepted Answer

Middle-infrared (2.5–25 µm)

Question 2

What is the primary requirement for a molecular vibration to be IR-active?

Accepted Answer

It must cause a change in the molecular dipole moment.

Question 3

A sample of hexanoic acid shows a broad absorption between 2500–3300 cm⁻¹ in its IR spectrum. Which functional group is responsible for this absorption?

Accepted Answer

Carboxylic acid O–H

Question 4

Which of the following is the correct order of intensity for carbon bond absorptions in IR spectroscopy?

Accepted Answer

C–O \u003e C–Cl \u003e C–N \u003e C–C–OH \u003e C–C–H

Question 5

Which equation describes the relationship between wavenumber ($$
u$$), wavelength ($$\lambda$$), and speed of light ($$c) in IR $$spectroscopy?

Accepted Answer

$$
u = \frac{1}{\lambda}$$

Question 6

Why is potassium bromide (KBr) commonly used in the preparation of solid samples for IR spectroscopy?

Accepted Answer

It transmits radiation across much of the mid-IR region.

Question 7

Which component in an IR spectrometer selects individual wavelengths of IR radiation?

Accepted Answer

Monochromator

Question 8

A molecule absorbs IR radiation at 1721 cm⁻¹. Which functional group is most likely present?

Accepted Answer

Carbonyl (C=O)

Question 9

Which of the following is a limitation of IR spectroscopy?

Accepted Answer

Overlapping absorption bands can complicate interpretation.

Question 10

In IR spectroscopy, why is water avoided as a solvent for liquid samples?

Accepted Answer

Water dissolves the NaCl or KCl sample cell.

Question 11

Which of the following best describes the principle of IR spectroscopy?

Accepted Answer

IR spectroscopy measures the absorption of infrared light by molecular bonds, causing vibrations.

Question 12

Which sample preparation method is most suitable for a dry solid sample in IR spectroscopy?

Accepted Answer

Grind with KBr and press into a pellet.

Question 13

Which of the following is NOT a strength of IR spectroscopy?

Accepted Answer

It is unaffected by water or other interfering substances.

Question 14

A molecule with a symmetrical bond, such as O₂, will:

Accepted Answer

Be IR-inactive because there is no change in dipole moment.

Question 15

Which of the following factors increases the intensity of IR absorption for a bond?

Accepted Answer

Greater change in dipole moment during vibration.

Question 16

Which IR region is used for quality control in the pharmaceutical industry?

Accepted Answer

Near-infrared (750–3000 nm)

Question 17

Which component of an IR spectrometer is responsible for measuring the IR radiation reaching it?

Accepted Answer

Detector

Question 18

Which of the following is a real-world application of IR spectroscopy?

Accepted Answer

Identification of raw materials in manufacturing

Question 19

Which functional group is indicated by a sharp absorption at 2210–2260 cm⁻¹ in an IR spectrum?

Accepted Answer

Nitrile (C≡N)

Question 20

Why is ATR-FTIR considered advantageous in sample preparation for IR spectroscopy?

Accepted Answer

It requires minimal sample preparation.

Infrared Spectroscopy (IR) in Analytical Chemistry: Principles, Instrumentation, and Applications

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