# How does mass spectroscopy of nicotine work?

Take this nicotine molecule:

And this mass spectrum:

I'm not sure how to explain all the peaks.

This might explain the peak at 42:

But can this peek als be explained by something else in the molecule?

Like the decomposition of the ring with the double bonds:

This might explain the peak at 84:

And I'm clueless on the peak at 133

The peak at 133 corresponds to a loss of 29 mass units (nicotine is 162). N-CH3 has a mass of 29

• How about the others? Do you think my guesses were correct? Commented Jan 26, 2014 at 4:35
• How can you know whether the peak at 42 is the decomposition of the ring with the double bonds or the ring without the double bonds? Commented Jan 26, 2014 at 9:18
• Yes, I think your other guesses are reasonable. As Klaus points out, you would need to look at the mass spectrum of some model compounds and/or some isotopically labeled compounds to know for sure. Also, especially in larger molecules, if you have a high resolution mass spectrometer that can help, because if you calculate the mass to 6 decimal places, different fragments with the same mass - but different formula - will give rise to different exact masses. As to which ring is fragmenting, the pyridine ring is aromatic and therefor has more stability then the saturated
– ron
Commented Jan 26, 2014 at 14:32
• pyrolidine ring, making the pyridine less likely to crack.
– ron
Commented Jan 26, 2014 at 14:33
• "pyrolidine ring, making the pyridine less likely to crack" How can you explain the fact that altghouh stable, there is no peak in the MS for 78... I would expect it to be the base peak. Commented Apr 17, 2018 at 6:38

I think that your assignment is reasonable.

As ron has already pointed out, cleavage of an endocyclic $\ce{C-N}$ bond (= opening of the pyrolidine ring) in nicotine is likely. The resulting open chain fragment then loses $\ce{NCH3}$.

The peak at 84 represents a N-methylpyrolidine fragment and indicates that the bond between the two heterocycles is cleaved. This also makes sense.

In general, it it a good idea to work from higher to lower masses and not to spend to much brain on the very small fragments.

• How can you know whether the peak at 42 is the decomposition of the ring with the double bonds or the ring without the double bonds? Commented Jan 26, 2014 at 9:17
• @Pickering You might be able to rule that out by comparison with the MS of pyridine. Further experimental proof could involve the specific isotopic labelling of the starting material. Commented Jan 26, 2014 at 9:27