MS newbe needs help with spectrum intepretation

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

6 posts Page 1 of 1
Dear experts,

attached you can find a spectrum I have obtained using GC-MS.
I've found traces of an unexpected substance in my product and since then I'm trying to relate the spectrum of this peak chemical structure of the substance.

My somewhat educated guess is also depicted in the spectrum. However, I'm having a hard time to explain the m/z 165 ion. I guess it might result from m/z 209 (which results from alpha cleavage) after loss of 44 (ethanal)? 165 being fluorene ion? Is it possible to definetly derive the position of the oxygen from this spectrum? Might also be attachted to the methyl group of toluene.

Any help is highly appreciated,
best regards


Image
One route to m/z 165 may be, where [m/z xxx]+. denotes the radical cation,

[m/z 286]+. loses 2 x H to form the basic carbonyl fluorene structure with
[m/z 284]+.

[m/z 284]+. loses CO to give the basic fluorene ring structure [m/z 256]+.

[m/z 256]+. loses the [C6H5CH2]. radical to give [m/z 165]+ ion.

Regards,
JMB

Edit: The m/z 105 signal locates the O atom where you have shown it.
JMB wrote:
One route to m/z 165 may be, where [m/z xxx]+. denotes the radical cation,

[m/z 286]+. loses 2 x H to form the basic carbonyl fluorene structure with
[m/z 284]+.

[m/z 284]+. loses CO to give the basic fluorene ring structure [m/z 256]+.

[m/z 256]+. loses the [C6H5CH2]. radical to give [m/z 165]+ ion.

Regards,
JMB

Edit: The m/z 105 signal locates the O atom where you have shown it.


Thank your very much for your input JMB!

However, shouldnt I be able to observe the mentioned ions in this case? Such as 284 and 256, which are missing completely in my spectrum? Even if they behave like intermediates?

Best Regards
A problem with the traditional presentation of a mass spectrum is that it leads to the,
A gives B, B gives C, C gives D, D gives E etc
as a sequential series, where A, B, C, D , E are CONSECUTIVE ions.This is what I gave you in my response.
In reality, the molecular ion can, and does usually, fragment via several concurrent pathways.
Another interpretation of your spectrum is that m/z 286 loses 91 to give m/z 195; This ion then loses 30 amu via a concerted mechanism to give m/z 165.
However, the m/z 165-167 cluster has an unusual appearance. Does m/z 195 lose CO to give m/z 167, which then eliminates H2 to give m/z 165?—-Possibly.
But then, how is m/z 166 formed at such high intensity?
Of course, I cannot prove that my interpretation is correct, any more than you can prove it is not. But I do think it more reasonable than loss of CH3CHO from m/z 209.

Regards,
JMB
Hi.

I am very sorry not to have read this post on the date it was, but nevertheless, I gave myself the task of making a proposal that I put in consideration for you in order to explain the fragment m / z 165.

I need to know one thing, How can I put a image?
This is my proposal, for the explanation of the ion m / z 165.



Image

Best Regards

HL
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