Mass Spec- breaking the benzene ring

In summary, the conversation discusses the molecular formula and mass spectrum of a compound, with a focus on obtaining structures representing peaks at 91, 118, and 65. The suggested structures involve a benzene ring and various attached groups, with a question raised about the possibility of breaking the benzene ring. A hint is given to consider the tropylium ion as the fragment, leading to a final solution.
  • #1
leah3000
43
0

Homework Statement


the molecular formula of the compound under analysis is C8H8O2 = Mr of 136
the mass spectrum shows the peak at 91 to be the most stable. I'm supposed to obtain structures representing the peak at 91 as well as at 118 and 65


The Attempt at a Solution



I represented 91 as the benzene ring with H-C(-H) attached

@ 118 H-C-C(=O) is attached

I'm having trouble getting the structure at 65

C8H8O2 would be represented as the benzene ring with H-C(-H)-C(=O)-O-H attached.
The only way I'm seeing to obtain 65 is if i remove the attached group from C8H8O2 along with a C from the benzene ring. Is this even possible? Because I know the benzene ring is very stable...:confused:
 
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  • #2
Are you positive this compound contains a benzene ring?

Could it be a cyclopentadiene or fulvene derivative?
 
  • #3
PhaseShifter said:
Are you positive this compound contains a benzene ring?

Could it be a cyclopentadiene or fulvene derivative?

well...those groups aren't on the syllabus I'm studying. Benzene and phenol are the only aromatic compounds I'm studying. Can benzene be an option?
 
  • #4
leah3000 said:

Homework Statement


the molecular formula of the compound under analysis is C8H8O2 = Mr of 136
the mass spectrum shows the peak at 91 to be the most stable. I'm supposed to obtain structures representing the peak at 91 as well as at 118 and 65


The Attempt at a Solution



I represented 91 as the benzene ring with H-C(-H) attached

@ 118 H-C-C(=O) is attached

I'm having trouble getting the structure at 65...

It's not benzene anymore... it's tropylium (m=91).
 
  • #5
chemisttree said:
It's not benzene anymore... it's tropylium (m=91).

I don't understand:confused:

maybe i explained it wrong? i was trying to describe the structure i assumed the fragments to be. But what I'm not clear on is if it's ever possible to break the benzene ring. I know the ring is stable due to the delocalised electrons...so I don't understand why the benzene ring itself would fragment. I have no idea as to what other solution it could be. :redface:
 
  • #6
leah3000 said:
...I'm not clear on is if it's ever possible to break the benzene ring.

That's why I gave you a hint... tropylium ion. Very interesting fragmentary pattern for tropylium ion... nuff said.

I know the ring is stable due to the delocalised electrons...so I don't understand why the benzene ring itself would fragment. I have no idea as to what other solution it could be. :redface:
See above.

hint: google "tropylium fragmentary pattern"
 
  • #7
thank you!
 
  • #8
De nada!
 

Related to Mass Spec- breaking the benzene ring

1. What is mass spectrometry?

Mass spectrometry is an analytical technique used to identify and quantify the chemical composition of a sample. It involves ionizing the sample molecules and separating them based on their mass-to-charge ratio.

2. How does mass spec break the benzene ring?

Mass spectrometry can break the benzene ring by using either electron ionization or chemical ionization techniques. These methods cause the benzene ring to fragment into smaller pieces, which can then be analyzed to determine the structure of the original molecule.

3. What are the benefits of breaking the benzene ring using mass spec?

Breaking the benzene ring using mass spectrometry allows for the identification and characterization of complex molecules. It also provides valuable information about the structural and chemical properties of the molecule, which can aid in drug development, environmental analysis, and other scientific studies.

4. Are there any limitations to using mass spec to break the benzene ring?

While mass spectrometry is a powerful tool for analyzing molecules, there are some limitations when it comes to breaking the benzene ring. For example, the fragmentation pattern of the ring may vary depending on the ionization method used, and some compounds may not produce a detectable fragment ion at all.

5. How is mass spectrometry used in environmental studies to break the benzene ring?

Mass spectrometry is commonly used in environmental studies to analyze air, water, and soil samples for the presence of benzene and other pollutants. By breaking the benzene ring, researchers can identify and quantify the amount of benzene present in the sample, which can help assess the level of environmental contamination and potential health risks.

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