This is the n-phenethylacetamide mass spectrum enter image description here

enter image description here

His base peak ion is at 104 m/z. I have long been thinking about what its structure might be, but with a m/z ratio of 104 I can not think of anything plausible. Can you help me?

Thanks in advance


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  • 1
    $\begingroup$ What ionisation method was used? $\endgroup$ – Waylander Jun 7 '18 at 12:42
  • $\begingroup$ @Waylander With so much fragmentation it will have been electronic impact $\endgroup$ – Raoul Kessels Jun 7 '18 at 14:00
  • $\begingroup$ Source Temperature: 200 °C, Sample Temperature: 150 °C, RESERVOIR: 75 eV $\endgroup$ – user3204810 Jun 7 '18 at 16:01
  • $\begingroup$ @Waylander Done! Long time since I did MS :-| $\endgroup$ – Raoul Kessels Jun 8 '18 at 14:57

Assuming electronic impact, the most electronegative atom will loose an electron and remain positively charged. Amides typically undergo a McLafferty rearrangement. In this case, the rearrangement can only be to one side, because the other chain is too short.

A neutral fragment of acetamide is lost (in its enolic form) and a positively charged styrene ion remains:

$\ce{C6H5-CH=CH2^+}$: $77+13+14=104$

The rearrangement is as follows:

enter image description here

(Sorry, I do not have a proper chemical drawing program with me; the arrows have been drawn on the touchscreen.)

  • $\begingroup$ That fits nicely $\endgroup$ – Waylander Jun 8 '18 at 15:01
  • $\begingroup$ Well: so, is a styrene ion? $\endgroup$ – user3204810 Jun 11 '18 at 12:08

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