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Describe nitrogen rule and even electron rule as applied in mass spectrometry. XI.
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The Nitrogen Rule states that a compound with an odd number of nitrogen atoms will have an odd-numbered molecular ion (M+) peak in its mass spectrum. Conversely, a compound with an even number of nitrogen atoms will have an even-numbered M+ peak. This rule is based on the fact that nitrogen has an odd number of valence electrons (5), and therefore its contribution to the total number of valence electrons in a molecule will either increase or decrease the odd/even nature of the molecule's overall number of electrons. This is directly related to the Even Electron Rule which states that fragments with an odd number of electrons are less stable and therefore less likely to be observed in the mass spectrum. This is because fragments with even numbers of electrons are more likely to be neutral or have a closed-shell electron configuration, making them more stable. In summary, the nitrogen rule helps us predict the odd/even nature of the molecular ion, and the even electron rule helps us understand the stability of the fragments observed in the mass spectrum.
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