Funky EIMS spectra -- help me interpret?

Hi,

This is for a lab assignment for university. We ran 1H-NMR, 13C-NMR, and EIMS on what is suspected to be 3-(4-chlorophenyl)propanoic acid. The NMRs confirmed its identity and no impurities were seen. The EIMS however...

Here we have the EIMS for the product (3-(4-chlorophenyl)propanoic acid):


And here for the precursor (4-chlorocinnamic acid):


The precursor looks fine. I can't figure out what's going on with the product, though.

These spectra were produced by university technicians and I am sure my professors/TA's would have spotted if something was off.

Any help?

Thanks,

Quote: Originally posted by Metacelsus

Wow, those spectra claim to be older than I am! My best guess is that what you have is 3-phenylpropanoic acid. You lost the chlorine somewhere. Was this a hydrogenation? Most of the fragments don't have chlorine (judging by M+2 peak intensity). The fragment at 150 is 3-phenylpropanoic acid minus a hydrogen atom. The fragment at 91 is C6H5-CH2. If you had a chlorine still, you would expect to see a fragment at 125 and M+2 at 127, for C6H4Cl-CH2. This is present in the bottom spectrum but not the top one. The lack of a parent ion around 184 is another clue. Can you also post the NMR data? [Edited on 2021-3-8 by Metacelsus]

Didn't notice the date. It might actually be that old -- due to COVID we're doing online lab now, and I think they're just reusing old spectra from previous years of doing this experiment.

Yes this was a hydrogenation of the cinnamic acid over Pd/C with ammonium formate.







Now that you mentioned it, the loss of chlorine actually makes sense. I wrote off that 2.5 on the spectra as just bad integration or possibly impurity, but it's very likely the Cl got hydrogenated away!