Question

Carbonyl (C=O) stretching vibration appears around

• A. 1000 cm⁻¹
• B. 1500 cm⁻¹
• C. 1700 cm⁻¹
• D. 3000 cm⁻¹

Hint:

In infrared (IR) spectroscopy, each type of bond absorbs IR radiation at a characteristic frequency, measured in wavenumbers (cm −1 ).

Answer 1

The Correct Option is C

Concept:
In infrared (IR) spectroscopy, each type of bond absorbs IR radiation at a characteristic frequency, measured in wavenumbers (cm⁻¹). This question asks you to recall where the carbonyl group shows up, which is one of the most useful diagnostic peaks in IR.

Step 1: The carbonyl group (C=O) is a strong, polar double bond. When it stretches, it gives a sharp and intense absorption band that is easy to spot in an IR spectrum.

Step 2: This characteristic C=O stretching band appears around 1700 cm⁻¹ (typically in the 1650–1750 cm⁻¹ region depending on the exact compound such as aldehydes, ketones, acids or esters).

Step 3: The other values point to different bonds — for example, around 3000 cm⁻¹ we see C–H and O–H stretches, while lower values near 1000–1500 cm⁻¹ relate to C–O, C–C and bending vibrations. So the carbonyl stretch is best matched to 1700 cm⁻¹.

Answer: Option (3) — 1700 cm⁻¹.