[hans50316]

Now I'm following steps as drawn below, and I have a mass spectrum of my product. However, I'm confused about the result. The following is my understanding of it:

1. No M⁺/M²⁺peaks have equal  heights, which means no Br.

2. If m/z=447 is molecular ion, the percentage of m/z=448 is 7.12, that means this compound has 6 or 7 carbons. But as m.w=447 with only 6~7 carbons, I think it's not reasonable.

3. If m/z=149 is molecular ion, with 13.67% of M⁺, it could contain 12 carbons, then 149-12*12=5, still not reasonable.

Here's the mass spectrum:  http://imgur.com/qvKhmOJ

So, do I misunderstand something?

[mjc123]

m/z 448 is 7% of the height of the highest peak i.e. 149. 448 is actually about a third of the height of 447, which is the ratio that matters.

[hans50316]

I think I forgot to transfer height into relative height first.
So, the m.w of my compound is 372.14, and I do have a peak at 372 with almost same height as peak at 374.
However, their intensity compare to the basic peak is only 1%. In this case, can I still analyze this way?

[MOTOBALL]

If m/z 447 is your molecular ion, then as mjc123 notes, it is the ratio of 448/447 intensities that you work with.

There are only two other things that you need to solve this..

1.  Study the "accounting" information, i.e. the printed header info at the top of the mass spectrum.

2. Write out the Nitrogen Rule for yourself, and its corollary.

Good Luck.

[MOTOBALL]

Were you told explicitly how the sample was analyzed ?

If not, ask your TA/prof. for the experimental details regarding the "accounting" info.

[hans50316]

The sample was ionized by FAB technique, so I probably get pseudo molecule ion which has m/z value larger than molecular ion by one.
Therefore, in this case, the nitrogen rule will be opposite.
Am I correct with this idea?

[MOTOBALL]

Well, not opposite exactly but I see what you mean.

Take your (M+H)+ value and get Mol Wt from this; apply the Nitrogen Rule to the Mol Wt value.

Consider how the sample is prepared for FAB-MS analysis !

Good Luck.