Nitrogen rule, mass spectra

The nitrogen rule of mass spectrometry says that a compound with an odd number of nitrogen atoms has an odd-numbered molecular weight. Thus, the presence of nitrogen in a molecule is detected simply by observing its mass spectrum. An odd-numbered molecular ion usually means that the unknown... 

Examples To rationalize the mass spectrum of methane, reactions 6.2-6.6 were proposed. They all obey the mle. You should check the mass spectra and fragmentation schemes throughout this chapter for additional examples of the nitrogen rule ... 

In the chemical ionization mass spectrum of pentobarbital in Figure 22-4, the peak with the most significant intensity at the high end of the mass spectrum at mlz 227 is suspected to be MH+ If this is so. then the nominal mass of M is 226. The nitrogen rule tells us that a molecule with an even mass must have an even number of nitrogen atoms. If you know from elemental analysis that the compound contains only C, H. N. and O. how many atoms of carbon would you suspect are in the molecule ... 

Thermal effects caused by the heating of the sample to volatilize it into the mass spectrometer have been studied by several groups of workers. Anomalous M+ 14 ions in the mass spectrum of the alkaloid, voacamine, were shown by deuterium labelling to be due to intermolecu-lar methyl transfer from a carbomethoxy group to, probably, a basic nitrogen atom (Thomas and Biemann, 1965). The intensity of the M +14 peak varied with vapourization temperature, but not sample pressure which tends to rule out an ion-molecular reaction. 

In the case of monoamines, if the molecular-ion peak is present, it appears at an odd mass number in the spectrum. In the case of other nitrogen compounds also, it appears at odd mass number when the compound contains an odd number of nitrogen atoms (the nitrogen rule). 

The effect of N atoms on the mass of the molecular ion in a mass spectrum is called the nitrogen rule A compound that contains an odd number of N atoms gives an odd molecular ion. A compound that contains an even number of N atoms (including zero) gives an even molecular ion. Two street drugs that mimic the effects of heroin illustrate this principle 3-methylfentanyl (two N atoms, even molecular weight) and MPPP (one N atom, odd molecular weight). 

Figure 6.11 UPLC QqTOF MS chromatograms of a tylosrn (4.1 p.g/kg, RSD = 1.5%, n = 3) incurred honey sample (CE—collision energy). Plots A and C traces of tylosin A. Plots B and D traces of tylosin B. Plots A2—spectrum at 4.42 min from plot A1 Plot B2—spectrum at 3.88 min from Bl plot C2—spectrum at 4.43 min from plot Cl. Plot D2—spectrum at 3.87 min from plot D1. Proposed fragmentation is based on the nitrogen rule and accurate mass measurement. (Reproduced and modified from Wang and Leung ° with permission from the Canadian Food Inspection Agency published by John Wiley Sons copyright 2007. Crown in the right of Canada.)...

The effect of N atoms on the mass of the molecular ion in a mass spectrum is called the nitrogen rule A compound that contains an odd number of N atoms gives an odd molecular ion. 

Important OE ions are even less probable in the lower-mass end of the spectrum thus intense even-mass peaks in this region are usually due to ions containing an odd number of nitrogen atoms, such as CH4N", mjz 30 (Mun, 1981). Similar reasoning leads to a corollary of the nitrogen rule ... 

The nitrogen rule states that if a molecule has an odd number of nitrogen atoms, it will have an odd molecular weight. The rule derives from the fact that nitrogen is unique among common elements/isotopes in having an odd valency but an even atomic number. Figure 5.20 shows the mass spectrum of aniline, with M+ at m/z 93. 

This broad band at 1500 cm was ascribed by Kaufman. Metin, and Saper-stein [10], to an IR observation of the amorphous carbon Raman D and G bands. This is forbidden by the selection rules, and has been attributed to the symmetry breaking introduced by the presence of CN bonds in the amorphous network. As carbon and nitrogen have different electronegativities, the formation of CN bonds gives the necessary charge polarity to allow the IR observation of the collective C=C vibrations in the IR spectrum. This conclusion was stated by the comparison of spectra taken from films deposited from N2 and N2. In the N2-film spectrum, no shift was observed for the 1500-cm band, whereas all other bands shifted as expected from the mass difference of the isotopes. Figure 25 compares... 

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