Question

Infrared (IR) spectroscopy is used for determining certain aspects of the structure of organic compounds. Which of the following statement(s) is/are FALSE?

• A. IR radiation induces electronic transitions
• B. IR peak intensities are related to molecular mass
• C. Most organic functional groups absorb in a characteristic region of the IR spectrum
• D. Each element absorbs at a characteristic wavelength

Hint:

IR spectroscopy = {vibrational} transitions. UV–Vis = {electronic} transitions. Peak position tells you {bond type}, not molecular mass.

Answer 1

The Correct Option is A, B, D

Step 1: Recall the principle of IR spectroscopy.
IR spectroscopy measures molecular vibrations (stretching and bending) caused by the absorption of infrared radiation.
It does not involve electronic transitions, which occur in UV-visible spectroscopy.
Step 2: Analyze each statement.
(A) False — IR causes vibrational, not electronic transitions.
(B) False — Peak intensity depends on change in dipole moment, not molecular mass.
(C) True — Functional groups have characteristic absorption frequencies (e.g., C=O at 1700 cm$^{-1}$).
(D) False if taken literally for elements, but in context of compounds, functional groups show characteristic absorption.
Step 3: Conclusion.
The false statements are (A) and (B).