elham90794
Registered: 09/26/09
Posts: 51
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Reply with quote | #1 |
I am a little confused. If m/z is odd then there absolutely must be a Nitrogen in the formula? For example for question 6c is C10H13O not possible because there are no Nitrogens? |
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Madeline
Registered: 10/10/09
Posts: 38
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Reply with quote | #2 |
The nitrogen rule states that if m/z is even, then there are an even number of nitrogens in the formula (this includes 0). If m/z is odd, then there are an odd number of nitrogens in the formula.
So yes, if m/z is odd there must be one or more nitrogens in the formula because 1 is the lowest odd positive integer. In 6c, C10H13O is not possible because the nitrogen count is 0, which is an even number, whereas the m/z tells us that there must be an odd number of nitrogens in the formula.
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JKim
Registered: 10/08/09
Posts: 12
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Reply with quote | #3 |
What Madeline said is correct, if the m/z ratio is odd, you can always expect at least 1N.
What I recommend doing when solving mass spectrometry problems is to make tables like they do in the think book. Write every possible molecular formula you can get and once you finish, recheck each formula with the H rule and the N rule. It might seem trivial, but it takes only a few seconds, and can help you avoid any careless errors. Since these molecular formulas will be used in IR and NMR, it really helps to avoid errors in the beginning of solving spectroscopy problems.
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