If you have a mass spec with an M+, M+2, and M+4 peak how do you determine the number of carbons?

asked by @ma23965 • almost 2 years ago • Organic Chemistry • 5 pts
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1 answer

Hey there!

Actually none of those peaks will tell you exactly how many carbons there are. At some point you are going to have to make an educated guess. All we know from this information is:

  • M+2 and M+4 = There are 2 halogens present in this molecule -Cl and/or -Br
  • M+ = The total atomic weight of the molecule

You can use a combination of this information to make an educated guess of how many carbons, chlorines, and or bromines exist in the molecule.

Here is a practice problem of me using the M+2 and M+4 peaks to relate to a molecule with 2 halogens on it. https://www.clutchprep.com/organic-chemistry/mass-spect-isotopes/?c_id=3592#content-item-5069

Hope this helps!

answered by @johnny • almost 2 years ago