Question

What will be the \(m/z\) value of the base peak in the mass spectrum of n-butyl benzene \((PhCH_2CH_2CH_2CH_3)\)?

• A. 57
• B. 77
• C. 91
• D. 134

Hint:

Alkylbenzenes fragment at the benzylic bond to give the stable tropylium cation.

Answer 1

The Correct Option is C

Check mass loss for each option: m/z 91 requires losing propyl radical (43), giving stabilized tropylium ion - favored. Others require less favorable losses (phenyl unit, butyl to unstabilized phenyl cation).

\[\boxed{(C)\ 91}\]