Question

Which of the following set of peaks (m/z) appears in the mass spectrum of 2-pentanone?

• A. m/z = 86, 71, 43, 15
• B. m/z = 86, 57, 29
• C. m/z = 86, 71, 58, 43, 15
• D. m/z = 86, 57, 29, 15

Hint:

In mass spectrometry, the molecular ion peak is the highest m/z value, and fragmentation peaks correspond to the loss of small groups like CH3 and CH2CH3.

Answer 1

The Correct Option is B

Step 1: Mass Spectrum of 2-Pentanone.
In the mass spectrum of 2-pentanone, the molecular ion (M+) peak is at m/z = 86. This corresponds to the molecular weight of 2-pentanone. The main fragmentation pattern occurs due to the loss of groups like CH3 (m/z = 15), CH2CH3 (m/z = 29), and smaller ions like m/z = 57.

Step 2: Conclusion.
Thus, the correct set of peaks is m/z = 86, 57, 29, which corresponds to option (2).

Final Answer: \[ \boxed{\text{(2) m/z = 86, 57, 29}} \]