Topic: Mass spectrum of a compound with M+ 224 and base peak 105 (Read 8131 times)

anya44995 · « **on:** May 21, 2012, 10:08:55 AM »

I have to identify an unknown organic compound through a multitude of tests and an analysis of the mass spectrum. The compound tested positive in a ferric chloride test, so it contains a phenol or an enol group. However, I think its mass spectrum indicates otherwise. Its M+ peak is at 224 (with a very high peak right next to it at 223), its second peak is at 147, its base peak is at 105 (with no peak at 94), and it also peaks at 77, 69, and 51. Do these numbers necessarily contradict the findings of the ferric chloride test? If not, what could this compound possibly be?

fledarmus · « **Reply #1 on:** May 21, 2012, 10:20:44 AM »

What about the mass spec convinced you that there was no phenol or enol present in the molecule? Or do you already have a molecule in mind that fits all the data except that it has no phenol or enol?

anya44995 · « **Reply #2 on:** May 21, 2012, 10:50:48 AM »

I'm not sure what to make of the loss of 77 between 224 and 147. Doesn't that usually correspond to a phenyl group? Also, I'm pretty sure that a base peak of 105 tends to indicate ethylbenzene (or a variant) somewhere in the compound. I am just not sure where the phenol/enol comes into play here.

fledarmus · « **Reply #3 on:** May 21, 2012, 11:10:44 AM »

That 105 could also be a benzylcarboxy fragment...

anya44995 · « **Reply #4 on:** May 21, 2012, 11:44:17 AM »

I guess I should have mentioned that I also have an IR spectrum of the molecule, and it does not have the characteristic broad loop around 3200 that molecules with OH usually exhibit. I know there are exceptions to this rule but doubt that my high school chemistry teacher would expect us to know this.

anya44995 · « **Reply #5 on:** May 21, 2012, 12:03:52 PM »

And also, the compound failed a bicarbonate test so it does not have a carboxyl group in it.

fledarmus · « **Reply #6 on:** May 21, 2012, 01:01:16 PM »

Have you done any test for a carbonyl group?

Anything else you can get from your IR?

And does the MS look like this...

fledarmus · « **Reply #7 on:** May 21, 2012, 01:19:17 PM »

I'm sorry, bad description earlier - that should have been a phenylcarbonyl, not a benzylcarboxy. I thought I edited that before it posted...

anya44995 · « **Reply #8 on:** May 21, 2012, 01:21:49 PM »

It looks quite similar but not identical to that one. Anyway, I've figured out that the compound is dibenzoylmethane (so it does have the two phenyl groups that I originally thought were in there, and the phenyl carbonyl groups too!)

I suppose now the follow up question is why this molecule tested positive in ferric chloride

fledarmus · « **Reply #9 on:** May 21, 2012, 01:43:12 PM »

Because of the tautomeric form with one ketone and one enol. This is very common in beta-diketones.

anya44995 · « **Reply #10 on:** May 21, 2012, 02:09:42 PM »

Great, thank you!

Topic: Mass spectrum of a compound with M+ 224 and base peak 105 (Read 8131 times)

anya44995

Mass spectrum of a compound with M+ 224 and base peak 105

fledarmus

Re: Mass spectrum of a compound with M+ 224 and base peak 105

anya44995

Re: Mass spectrum of a compound with M+ 224 and base peak 105

fledarmus

Re: Mass spectrum of a compound with M+ 224 and base peak 105

anya44995

Re: Mass spectrum of a compound with M+ 224 and base peak 105

anya44995

Re: Mass spectrum of a compound with M+ 224 and base peak 105

fledarmus

Re: Mass spectrum of a compound with M+ 224 and base peak 105

fledarmus

Re: Mass spectrum of a compound with M+ 224 and base peak 105

anya44995

Re: Mass spectrum of a compound with M+ 224 and base peak 105

fledarmus

Re: Mass spectrum of a compound with M+ 224 and base peak 105

anya44995

Re: Mass spectrum of a compound with M+ 224 and base peak 105

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