Question

Which of the following compounds shows a sharp band at 2150 cm$^{-1}$ and 3300 cm$^{-1}$ in the IR spectrum?

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

In IR spectra, alkyne C≡C stretches appear around 2150 cm$^{-1}$, and N-H stretches typically appear around 3300 cm$^{-1}$.

Answer 1

The Correct Option is A

Step 1: IR Absorption Bands.
- A sharp band around 2150 cm$^{-1}$ is characteristic of a C≡C stretch (alkyne), while a broad band around 3300 cm$^{-1}$ is characteristic of an N-H stretch (amines).

Step 2: Analysis of Options.
- (1) Alkyne (\( \text{C} \equiv \text{H} \)) shows the sharp band at 2150 cm$^{-1}$ and a stretch at 3300 cm$^{-1}$ due to the C-H stretch. This matches the given conditions.
- (2) Alkene (\( \text{C} = \text{C} \)) would show a different stretch and does not match both bands.
- (3) Amines (\( \text{N-H} \)) show a broad stretch near 3300 cm$^{-1}$ but not the 2150 cm$^{-1}$ band.
- (4) Amine (\( \text{H}_2\text{N} \)) would only show a broad N-H stretch without the C≡C stretch.

Step 3: Conclusion.
Thus, the correct answer is (1) Alkyne (\( \text{C} \equiv \text{H} \)).

Final Answer: \[ \boxed{\text{(1) Alkyne (C≡H)}} \]