[s3432693]

I've been given a set of spectra for an unknown molecule and have been assigned to determine the structure. I've determined my structure to be 4-chlorobenzamide, in the mass spectrum there is a relatively large intensity peak at m/z 75 and I cant seem to fragment my molecule in anyway to produce this m/z value. Here's a link to the spectrum I've found on the AIST website, you'll need to click on the mass button on the left hand of the page to see the mass spectrum http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_disp.cgi?sdbsno=1407 , What fragment does m/z 75 come from?

The molecular ion is at m/z 155, why are there small signals at approx. m/z 175 and 195? Is this due to left over ions from a previous experiment in the mass spectrometer? Finally, why is there no m/z 35 for the fragmentation of chlorine from the molecule? Is this an unfavourable fragmentation?

Thank You

[Burner]

The peak of m/z=75 should come from the stripping off of -CONH₂ group and the -Cl group, as normally you can't fragmentate a benzene ring.

[s3432693]

Removal of -CONH₂ and -Cl would give an m/z of 76 and there should also a peak at m/z 35 for the chlorine which isn't present in the spectra

[MOTOBALL]

List out the m/z values in the spectrum from 155 down.
What is the mass difference between each successive ion ?
What combination of atoms gives that mass ?
What is the mass difference between m/z75 and next higher ion ?
What is the difference in the appearance between the m/75 ion and the m/z 155 ion ?