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I appreciate Karsten Theis for his effort to solve this problem, but I have to say that I completely disagree with the structure he has come with as the answer (as a matter of fact, I came up with the same structure but it didn't fit the given $\ce{^1H}$-$\mathrm{NMR}$ spectrum; vide infra). Followings are my reasons:
As correctly pointed out by Karsten ...
3
Taking the hint from your instructor and the 13-C signal at 175 ppm fits nicely to a $\ce{-CH2-CO-O-CH2-CH3}$ fragment, i.e an ester. The 13-C spectrum shows only 6 peaks and the molar mass is about 258 g/mol, so there is probably some symmetry in the molecule.
There is something that puzzles me. The signals around 1.2 ppm in the proton NMR integrate to 3.5, ...
1
You should not have a single sample preparation for all the elements. The sample preparation will depend on element by element. Your calculations have subtle misconceptions. Don't convert to concentrations but work with masses for such problems.
So, you have 15 $\mu$g Mn in 15 g sample. This means you have 1 $\mu$g Mn in 1 g sample (see, I am avoiding ...
1
This situation is not uncommon. A mass spectrometer has no way of knowing the absolute mass or absolute charge of ions. Suppose compound A has a peak that appears at $m/z$. You suggest another compound B, which has $2m/2z$ or $nm/nz$. This is the only condition where you will see a peak overlap in MS. Note, $m$, is the nominal mass. Exact masses, measurable ...
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