[remeday86]

This is under the subject of Mass spectrometry. I know how to determine the possible molecular formulas of an even molecular ion, but not on the ODD.

Propose two or more molecular formula for the molecular ion of 73:

My work:
I know that the molecular ion is at m/z = 73. Which also means that the molecular weight of a compound is equal to the mass of the molecular ion.

so now...This is an ODD molecular ion which means it must contain an N atom.
Therefore, I did the following:
73-14 = 59
59/12 = 4 remainder 11
Therefore, a possible molecular formula is C4H11N

The answers in the book are C4H11N and C2H7H3.

I don't know how to get the second one.
Please help and show it step by step. I would like to apply the steps next time I encounter an ODD molecular ion.
Thanks in advance!

[Dan]

so now...This is an ODD molecular ion which means it must contain an N atom.

Yes, but more generally the structure could contain an odd number or N atoms.

See Nitrogen "rule"

The answers in the book are C4H11N and C2H7H3.

This should be C₂H₇N₃ - an odd number of N atoms.

If you go through the same process you used for C₄H₁₁N, but with 3 N atoms rather than 1, you will arrive at the solution C₂H₇N₃

There are many solutions though, for example: C₂H₃O₂N or C₃FH₄N etc. etc.

[remeday86]

Ok thanks. I understand now.