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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Elnino on October 21, 2013, 11:02:26 PM

Title: GC/MS spectrum - phenyl thinochloroformate
Post by: Elnino on October 21, 2013, 11:02:26 PM

-Undergraduate researcher-

I reacted phenyl thinochloroformate with a aminoflavone in dry THF. The product weight is about 373. However this weight wasn't present on the GC/MS spectrum, only one peak present but it showed m/z of 279. Are thionocarbamates not detectable on GC/MS? I'm not quite sure what happened.

Thanks

Title: Re: GC/MS spectrum - phenyl thinochloroformate
Post by: kriggy on October 22, 2013, 01:30:22 AM

Could you show us the spectrum? Im not that experienced but it could me many things.

Title: Re: GC/MS spectrum - phenyl thinochloroformate
Post by: MOTOBALL on October 22, 2013, 10:50:57 AM

Your reaction product (MW 373) eliminated phenol (MW 94) to give the [ArN=C=S]+. ion
at m/z 279.

If you want to see the M+. ion you will have to run GC/MS with CH4 chemical ionization.

On older MS systems you could also lower the energy of the electron beam to reduce fragmentation, but I doubt that you have that option.

Title: Re: GC/MS spectrum - phenyl thinochloroformate
Post by: MOTOBALL on October 22, 2013, 11:19:39 AM

If you want to see the M+. ion you will have to run GC/MS with CH4 chemical ionization.

I should have said that if you want to determine the MW, you will have to run GC/MS with CH4 chemical ionization which should give the [M+H]+ protonated molecular ion.  Given the very facile loss of phenol under EI conditions, you may also see this to some degree under CI conditions.