Question

Compound(s) that show(s) an intense peak at \( m/z = 120 \) in the EI mass spectrum is/are:

• A.
• B.
• C.
• D.

Hint:

The \( m/z = 120 \) peak in EI mass spectra typically arises from the tropylium ion, commonly observed in compounds with benzyl or substituted aryl alkyl chains. Look for benzylic cleavage pathways.

Answer 1

The Correct Option is A, B, D

The intense peak at m/z = 120 in EI (Electron Impact) mass spectrometry often corresponds to the tropylium ion (C₇H₇⁺), a very stable aromatic cation. This ion is formed by the fragmentation of alkyl-substituted benzyl systems.

• (A) The compound is phenylbutanone. On EI ionization, it can lose the carbonyl side chain and rearrange to form the stable tropylium ion (m/z = 120). CORRECT
• (B) The structure is similar, with an isopropyl substitution. Fragmentation also allows formation of the tropylium ion. CORRECT
• (C) This is a salicylic acid derivative. No alkyl chain or benzylic system is available to form the tropylium ion. WRONG
• (D) This is methyl salicylate. On fragmentation, the ester moiety can allow tropylium ion formation via rearrangement. CORRECT

✅ Final Answer: Compounds (A), (B), and (D) show a peak at m/z = 120.