Question 1

Which fundamental principle allows FTIR spectroscopy to identify functional groups in organic compounds?

Accepted Answer

The absorption of infrared radiation is based on vibrational spectroscopy, which relates absorbed energy to frequency according to Planck's equation $E = h
u$.

Question 2

Given the equation for vibrational frequency $
u = \frac{1}{2\pi} \sqrt{\frac{k}{\mu}}$, what effect does increasing the bond force constant $k$ have on the IR absorption frequency?

Accepted Answer

It increases the absorption frequency.

Question 3

Why is it necessary to collect a background spectrum before every sample analysis in FTIR spectroscopy?

Accepted Answer

To remove the effects of atmospheric and instrumental absorption from the sample spectrum.

Question 4

A student observes a strong, broad absorption around 3200–3600 cm$^{-1}$ in an FTIR spectrum. Which functional group is most likely present?

Accepted Answer

Alcohol (O–H stretch)

Question 5

Which of the following is a common source of error that can cause irregular or low measurement readings in FTIR spectrometers?

Accepted Answer

Failure to clean the ATR crystal between samples.

Question 6

A sample shows a strong absorption at 1700 cm$^{-1}$ and a medium absorption at 2500–3300 cm$^{-1}$. Which compound is most likely present?

Accepted Answer

Carboxylic acid

Question 7

What is the main advantage of Fourier Transform Infrared (FTIR) spectroscopy over conventional dispersive IR instruments?

Accepted Answer

FTIR provides faster scanning, improved sensitivity, and higher resolution.

Question 8

If a compound shows a sharp absorption at 2250 cm$^{-1}$ in its FTIR spectrum, which functional group is most likely present?

Accepted Answer

Nitrile (C≡N stretch)

Question 9

Which region of the FTIR spectrum is typically used to identify characteristic functional group vibrations?

Accepted Answer

4000–1000 cm$^{-1}$

Question 10

A student is analyzing an unknown sample and observes two strong absorptions at 1600 cm$^{-1}$ and 1500 cm$^{-1}$, along with several peaks between 690–900 cm$^{-1}$. What is the most likely structure of the compound?

Accepted Answer

Aromatic ring

Question 11

Which maintenance procedure is essential for ensuring accurate FTIR measurements when using a diamond ATR sampling accessory?

Accepted Answer

Cleaning the diamond sampling window with acetone or alcohol after each use.

Question 12

Why do stronger bonds and lighter atoms vibrate at higher frequencies in IR spectroscopy?

Accepted Answer

Because the bond force constant $k$ is higher and the reduced mass $\mu$ is lower, as shown in $
u = \frac{1}{2\pi} \sqrt{\frac{k}{\mu}}$.

Question 13

Which of the following is NOT a recommended precaution when operating an FTIR spectrometer?

Accepted Answer

Overtighten the sample press knob to ensure a tight seal.

Question 14

A pharmaceutical company uses FTIR to verify the purity of a drug sample. Which feature of FTIR makes it suitable for this application?

Accepted Answer

FTIR provides a unique molecular fingerprint for each compound.

Question 15

Which of the following steps is required to collect a sample spectrum using a diamond ATR accessory?

Accepted Answer

Place a small amount of sample on the crystal, ensuring the material covers the entire surface.

Question 16

A student collects an FTIR spectrum and observes a strong absorption at 1720 cm$^{-1}$ and no significant peaks in the 3200–3600 cm$^{-1}$ region. Which functional group is most likely present?

Accepted Answer

Ketone (C=O stretch)

Question 17

Which of the following best describes the role of Planck's constant $h$ in FTIR spectroscopy?

Accepted Answer

It relates the energy of absorbed radiation to its frequency: $E = h
u$.

Question 18

Which type of sample preparation is most appropriate for FTIR analysis using the ATR accessory?

Accepted Answer

Placing a small amount of solid or liquid directly on the ATR crystal.

Question 19

A forensic scientist uses FTIR to analyze a paint chip from a crime scene. What property of FTIR makes it valuable for this application?

Accepted Answer

FTIR can provide a non-destructive analysis and a molecular fingerprint for identification.

Interpreting FTIR Spectra: Principles, Procedures, and Applications in Organic Chemistry

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