[elute96]

Hey,

I have an exam coming up where I'm required to sketch an approximate mass spectrum of an organic compound. Obviously it's quite easy to get the m/z of the fragments for each signal but how am I meant to know at what abundance they occur?

Is there a way to estimate them?

Thanks!

[wayne]

It's hard to estimate their abundance, and unnecessary, I think.

[fledarmus]

Normally it isn't necessary to estimate abundances of fragments, because they are so dependent on the configuration of the particular instrument. You do, however, need to be able to estimate the relative sizes of the M, M+1 (from natural abundance of ¹³C), and M+2 (from natural abundance of S, Cl, or Br isotopes), and any higher significant contributors (M+4 if there are multiple Br's, Cl's, or S's). For example, a fragment containing a Br atom would show two approximately equal sized peaks at M and M+2, and one containing two Br atoms would show an approx 1:2:1 ratio at M, M+2, and M+4.

(Note - I am using "M" very freely as meaning the molecular mass that shows up on your particular instrument - that may actually be the MW of the fragment, or one higher or lower depending on the ionization technique)

Hope that helps