Question

How many N-H Stretching bands observed in the IR spectrum of primary Amines ($R-NH_2$)?

• A. 0
• B. 1
• C. 2
• D. 3

Hint:

Primary ($NH_2$) = 2 bands; Secondary ($NH$) = 1 band; Tertiary (no H) = 0 bands.

Answer 1

The Correct Option is C

Step 1: Concept IR spectroscopy detects vibrational modes of functional groups.

Step 2: Meaning Primary amines have two hydrogen atoms attached to the nitrogen.

Step 3: Analysis These two N-H bonds can vibrate in two distinct ways: symmetric stretching and asymmetric stretching. This results in two closely spaced peaks in the $3300-3500~cm^{-1}$ region.

Step 4: Conclusion Therefore, 2 N-H stretching bands are observed. Final Answer: (3)